I was on the fence between both the One X and the GS3, and ended up going with the GS3. While using both of them for over an hour I just felt there was alot less lag on the GS3. And if the GS3 is this fast with ICS, just imagine how it will feel with JB when it gets pushed out.
I can't knock the One X for too many things though, the build quality basically stomps all over the GS3, the screen in day light is just lite years better, and the camera may be a tad better then the GS3.
But sense feels very heavy to me as an overlay, and just feels outdated IMO. And what's up with the multi tasking feature that basically missing on the US version, that's crazy that its not fixed yet. To me that was enough to just roll with Samsung right now.
Different strokes for different folks.