The 535 has 1 GB of RAM, meaning it'll run more games and apps. (although, not many - just the fancy ones) and has more features. (LED flash, larger display with more pixels, front facing camera)
The 630 is built better from what I see and has a higher quality (not necessarily as sharp or large though) display.
Generally the 535 is better on paper and in features, I think the 630 is more solid.
I know I'm missing a lot, but it's late and I better wrap up some other things.
I think the deciding factor is going to be the price.