I think the benefit of 64-bit are mostly theoretical, and not actual. At most, at some point in the future, the older 32-bit architecture apps will no longer receive updates. But right now, they both play files the same.
MPC is "better" simply because you can click it anywhere, or press the space bar, and it pauses.
With VLC, you have to find the little bitty || button. That's annoying to me.
I've caught VLC not following the colorspaces. VLC also does not want to play
Huffyuv AVI files. So it's just an all-around bad choice lately.