What I did:
The map, game type and win/loss of everyone's last 25 games is shown on their battle.net profile website. Courtesy of www.sc2ranks.com (thanks!), I mined through this match history of all EU Diamond players and gathered the win/loss for each 1v1 game (so only solo ladder is included, no custom games). Note that using this method, or any other I know, it's not possible to calculate specific matchup win percentages, as the opponent or their race is not shown. Also note that the system is not zero-sum (that is, the numbers don't "add up to 50%"), as 1) this includes games played by Diamond players against lower league players 2) this only includes everyone's last 0-25 1v1 matches (depending what types of games they have played lately).
I separately included the stats for players ranked 1-5000 on EU, and all EU Diamond players. Note that the former might not be statistically significant for all cases, and for random players neither is probably very statistically significant. I've highlighted some of the results that struck me as interesting, either because the result differs from my understanding of the "mainstream opinion", or because the result is even better/worse than people might think (like the Zerg highlights). Come into your own conclusions! Hope the other statistics nuts around get their daily fix on this

All EU Diamond players with mirror match bias removed:
+ Show Spoiler +
Terran on Lost Temple : 2813/4934 = 57.01%
Terran on Metalopolis : 2496/4501 = 55.45%
Terran on Kulas Ravine : 1713/3117 = 54.95%
Terran on Xel'Naga Caverns : 2606/4791 = 54.39%
Terran on Steppes of War : 2767/5134 = 53.89%
Terran on Desert Oasis : 1349/2514 = 53.65%
Terran on Delta Quadrant : 1686/3156 = 53.42%
Terran on Scrap Station : 1893/3637 = 52.04%
Terran on Blistering Sands : 2088/4175 = 50.01%
Zerg on Scrap Station : 2341/4097 = 57.13%
Zerg on Desert Oasis : 1359/2479 = 54.82%
Zerg on Blistering Sands : 2448/4476 = 54.69%
Zerg on Metalopolis : 2437/4573 = 53.29%
Zerg on Lost Temple : 2341/4444 = 52.67%
Zerg on Xel'Naga Caverns : 2366/4559 = 51.89%
Zerg on Steppes of War : 2336/4616 = 50.60%
Zerg on Kulas Ravine : 1235/2443 = 50.55%
Zerg on Delta Quadrant : 1424/2938 = 48.46%
Protoss on Desert Oasis : 1855/3415 = 54.31%
Protoss on Blistering Sands : 3337/6238 = 53.49%
Protoss on Xel'Naga Caverns : 3463/6512 = 53.17%
Protoss on Steppes of War : 3718/7000 = 53.11%
Protoss on Delta Quadrant : 2159/4071 = 53.03%
Protoss on Kulas Ravine : 2150/4067 = 52.86%
Protoss on Metalopolis : 3257/6164 = 52.83%
Protoss on Lost Temple : 3398/6608 = 51.42%
Protoss on Scrap Station : 2636/5128 = 51.40%
Terran on Metalopolis : 2496/4501 = 55.45%
Terran on Kulas Ravine : 1713/3117 = 54.95%
Terran on Xel'Naga Caverns : 2606/4791 = 54.39%
Terran on Steppes of War : 2767/5134 = 53.89%
Terran on Desert Oasis : 1349/2514 = 53.65%
Terran on Delta Quadrant : 1686/3156 = 53.42%
Terran on Scrap Station : 1893/3637 = 52.04%
Terran on Blistering Sands : 2088/4175 = 50.01%
Zerg on Scrap Station : 2341/4097 = 57.13%
Zerg on Desert Oasis : 1359/2479 = 54.82%
Zerg on Blistering Sands : 2448/4476 = 54.69%
Zerg on Metalopolis : 2437/4573 = 53.29%
Zerg on Lost Temple : 2341/4444 = 52.67%
Zerg on Xel'Naga Caverns : 2366/4559 = 51.89%
Zerg on Steppes of War : 2336/4616 = 50.60%
Zerg on Kulas Ravine : 1235/2443 = 50.55%
Zerg on Delta Quadrant : 1424/2938 = 48.46%
Protoss on Desert Oasis : 1855/3415 = 54.31%
Protoss on Blistering Sands : 3337/6238 = 53.49%
Protoss on Xel'Naga Caverns : 3463/6512 = 53.17%
Protoss on Steppes of War : 3718/7000 = 53.11%
Protoss on Delta Quadrant : 2159/4071 = 53.03%
Protoss on Kulas Ravine : 2150/4067 = 52.86%
Protoss on Metalopolis : 3257/6164 = 52.83%
Protoss on Lost Temple : 3398/6608 = 51.42%
Protoss on Scrap Station : 2636/5128 = 51.40%
Stats with bias included
+ Show Spoiler +
5000 best ranked EU Diamond players:
+ Show Spoiler +
Terran on Lost Temple : 1596/2849 = 56.01 %
Terran on Metalopolis : 1476/2638 = 55.95 %
Terran on Steppes of War : 1571/2830 = 55.51 %
Terran on Xel'Naga Caverns : 1401/2620 = 53.47 %
Terran on Desert Oasis : 596/1116 = 53.40 %
Terran on Scrap Station : 1037/1943 = 53.37 %
Terran on Delta Quadrant : 994/1864 = 53.32 %
Terran on Blistering Sands : 1144/2175 = 52.59 %
Terran on Kulas Ravine : 902/1715 = 52.59 %
Zerg on Scrap Station : 1327/2348 = 56.51 %
Zerg on Blistering Sands : 1344/2441 = 55.05 %
Zerg on Desert Oasis : 635/1177 = 53.95 %
Zerg on Metalopolis : 1452/2702 = 53.73 %
Zerg on Lost Temple : 1380/2580 = 53.48 %
Zerg on Xel'Naga Caverns : 1366/2593 = 52.68 %
Zerg on Steppes of War : 1295/2494 = 51.92 %
Zerg on Kulas Ravine : 682/1320 = 51.66 %
Zerg on Delta Quadrant : 824/1623 = 50.77 %
Protoss on Desert Oasis : 773/1386 = 55.77 %
Protoss on Xel'Naga Caverns : 1740/3153 = 55.18 %
Protoss on Kulas Ravine : 1118/2041 = 54.77 %
Protoss on Steppes of War : 1884/3504 = 53.76 %
Protoss on Delta Quadrant : 1210/2251 = 53.75 %
Protoss on Blistering Sands : 1674/3138 = 53.34 %
Protoss on Metalopolis : 1804/3386 = 53.27 %
Protoss on Lost Temple : 1870/3568 = 52.41 %
Protoss on Scrap Station : 1250/2458 = 50.85 %
Random on Blistering Sands : 309/546 = 56.59 %
Random on Steppes of War : 300/542 = 55.35 %
Random on Scrap Station : 255/462 = 55.19 %
Random on Delta Quadrant : 215/390 = 55.12 %
Random on Kulas Ravine : 194/352 = 55.11 %
Random on Desert Oasis : 144/263 = 54.75 %
Random on Xel'Naga Caverns : 270/512 = 52.73 %
Random on Metalopolis : 268/518 = 51.73 %
Random on Lost Temple : 256/529 = 48.39 %
Terran on Metalopolis : 1476/2638 = 55.95 %
Terran on Steppes of War : 1571/2830 = 55.51 %
Terran on Xel'Naga Caverns : 1401/2620 = 53.47 %
Terran on Desert Oasis : 596/1116 = 53.40 %
Terran on Scrap Station : 1037/1943 = 53.37 %
Terran on Delta Quadrant : 994/1864 = 53.32 %
Terran on Blistering Sands : 1144/2175 = 52.59 %
Terran on Kulas Ravine : 902/1715 = 52.59 %
Zerg on Scrap Station : 1327/2348 = 56.51 %
Zerg on Blistering Sands : 1344/2441 = 55.05 %
Zerg on Desert Oasis : 635/1177 = 53.95 %
Zerg on Metalopolis : 1452/2702 = 53.73 %
Zerg on Lost Temple : 1380/2580 = 53.48 %
Zerg on Xel'Naga Caverns : 1366/2593 = 52.68 %
Zerg on Steppes of War : 1295/2494 = 51.92 %
Zerg on Kulas Ravine : 682/1320 = 51.66 %
Zerg on Delta Quadrant : 824/1623 = 50.77 %
Protoss on Desert Oasis : 773/1386 = 55.77 %
Protoss on Xel'Naga Caverns : 1740/3153 = 55.18 %
Protoss on Kulas Ravine : 1118/2041 = 54.77 %
Protoss on Steppes of War : 1884/3504 = 53.76 %
Protoss on Delta Quadrant : 1210/2251 = 53.75 %
Protoss on Blistering Sands : 1674/3138 = 53.34 %
Protoss on Metalopolis : 1804/3386 = 53.27 %
Protoss on Lost Temple : 1870/3568 = 52.41 %
Protoss on Scrap Station : 1250/2458 = 50.85 %
Random on Blistering Sands : 309/546 = 56.59 %
Random on Steppes of War : 300/542 = 55.35 %
Random on Scrap Station : 255/462 = 55.19 %
Random on Delta Quadrant : 215/390 = 55.12 %
Random on Kulas Ravine : 194/352 = 55.11 %
Random on Desert Oasis : 144/263 = 54.75 %
Random on Xel'Naga Caverns : 270/512 = 52.73 %
Random on Metalopolis : 268/518 = 51.73 %
Random on Lost Temple : 256/529 = 48.39 %
All EU Diamond players (~19500):
+ Show Spoiler +
Terran on Lost Temple : 4325/7959 = 54.34 %
Terran on Metalopolis : 3876/7261 = 53.38 %
Terran on Kulas Ravine : 2668/5028 = 53.06 %
Terran on Xel'Naga Caverns : 4074/7728 = 52.71 %
Terran on Steppes of War : 4341/8282 = 52.41 %
Terran on Desert Oasis : 2120/4056 = 52.26 %
Terran on Delta Quadrant : 2653/5091 = 52.11 %
Terran on Scrap Station : 3008/5867 = 51.26 %
Terran on Blistering Sands : 3367/6734 = 50.0 %
Zerg on Scrap Station : 3350/6116 = 54.77 %
Zerg on Desert Oasis : 1970/3701 = 53.22 %
Zerg on Blistering Sands : 3551/6682 = 53.14 %
Zerg on Metalopolis : 3563/6826 = 52.19 %
Zerg on Lost Temple : 3436/6634 = 51.79 %
Zerg on Xel'Naga Caverns : 3489/6805 = 51.27 %
Zerg on Steppes of War : 3473/6891 = 50.39 %
Zerg on Kulas Ravine : 1837/3647 = 50.37 %
Zerg on Delta Quadrant : 2148/4386 = 48.97 %
Protoss on Desert Oasis : 2553/4811 = 53.06 %
Protoss on Blistering Sands : 4611/8786 = 52.48 %
Protoss on Xel'Naga Caverns : 4793/9173 = 52.25 %
Protoss on Steppes of War : 5148/9860 = 52.21 %
Protoss on Delta Quadrant : 2991/5735 = 52.15 %
Protoss on Kulas Ravine : 2981/5729 = 52.03 %
Protoss on Metalopolis : 4516/8682 = 52.01 %
Protoss on Lost Temple : 4748/9308 = 51.01 %
Protoss on Scrap Station : 3683/7223 = 50.98 %
Random on Steppes of War : 1107/2073 = 53.40 %
Random on Delta Quadrant : 736/1388 = 53.02 %
Random on Scrap Station : 952/1798 = 52.94 %
Random on Kulas Ravine : 698/1343 = 51.97 %
Random on Blistering Sands : 1032/2006 = 51.45 %
Random on Xel'Naga Caverns : 1018/1981 = 51.38 %
Random on Desert Oasis : 601/1177 = 51.06 %
Random on Metalopolis : 969/1916 = 50.57 %
Random on Lost Temple : 1017/2020 = 50.34 %
Terran on Metalopolis : 3876/7261 = 53.38 %
Terran on Kulas Ravine : 2668/5028 = 53.06 %
Terran on Xel'Naga Caverns : 4074/7728 = 52.71 %
Terran on Steppes of War : 4341/8282 = 52.41 %
Terran on Desert Oasis : 2120/4056 = 52.26 %
Terran on Delta Quadrant : 2653/5091 = 52.11 %
Terran on Scrap Station : 3008/5867 = 51.26 %
Terran on Blistering Sands : 3367/6734 = 50.0 %
Zerg on Scrap Station : 3350/6116 = 54.77 %
Zerg on Desert Oasis : 1970/3701 = 53.22 %
Zerg on Blistering Sands : 3551/6682 = 53.14 %
Zerg on Metalopolis : 3563/6826 = 52.19 %
Zerg on Lost Temple : 3436/6634 = 51.79 %
Zerg on Xel'Naga Caverns : 3489/6805 = 51.27 %
Zerg on Steppes of War : 3473/6891 = 50.39 %
Zerg on Kulas Ravine : 1837/3647 = 50.37 %
Zerg on Delta Quadrant : 2148/4386 = 48.97 %
Protoss on Desert Oasis : 2553/4811 = 53.06 %
Protoss on Blistering Sands : 4611/8786 = 52.48 %
Protoss on Xel'Naga Caverns : 4793/9173 = 52.25 %
Protoss on Steppes of War : 5148/9860 = 52.21 %
Protoss on Delta Quadrant : 2991/5735 = 52.15 %
Protoss on Kulas Ravine : 2981/5729 = 52.03 %
Protoss on Metalopolis : 4516/8682 = 52.01 %
Protoss on Lost Temple : 4748/9308 = 51.01 %
Protoss on Scrap Station : 3683/7223 = 50.98 %
Random on Steppes of War : 1107/2073 = 53.40 %
Random on Delta Quadrant : 736/1388 = 53.02 %
Random on Scrap Station : 952/1798 = 52.94 %
Random on Kulas Ravine : 698/1343 = 51.97 %
Random on Blistering Sands : 1032/2006 = 51.45 %
Random on Xel'Naga Caverns : 1018/1981 = 51.38 %
Random on Desert Oasis : 601/1177 = 51.06 %
Random on Metalopolis : 969/1916 = 50.57 %
Random on Lost Temple : 1017/2020 = 50.34 %