I personally don't prefer any of the above, but ex720 is a 3D TV. I would have a look at it before finalising. c630 is a better option within the given budget if not sony ex720.
The samsung 32c5000 LED is around 43K but w/o 100Hz Motion Plus.
I have gone for c630 coz of USB capability, 100Hz and more brightness (2,00,000:1).
If you get a chance of auditioning ex-520 and c630 side by side, you are good to make the best decision out of your mind.
Cheers,
Siva