Ven's speed means nothing. Larxene was the fastest Organization member and she lost to Sora. Come to think of it, Larxene and Ven are probably at the same level, so that would be a more even fight. But yeah, Sora's more skilled than Ven, plus Sora's reaction commands would just completely outclass Ven's skill-set. So...
But, seriously, Sora would win.
Official Luxord of the Kingdom Hearts: Birth By Sleep Board
Unfortunately, Sora is leagues above what we've seen of him. However, after he's made his return who knows the heights he'll reach.
So as of now, Sora. In the future, however, who knows? The main character doesn't necessarily have to be able to beat all of his companions, or even be the strongest, so it's not like he doesn't have a chance.