I don't think we can give you a good answer. The best thing is to play with both phones in the store or if you have friends with them.
Some people like the SGS3's plastic, others prefer the more solid feeling build of the HTC One X.
I personally picked the SGS3 for a number of reasons.
1. I like having extra batteries simply because I do a lot of field work and sometimes you go 3-5 days without an electricity source.
2. I take lots of pics so expandable memory is a must.
3. like point 2, it needs to have a good camera, i take lots of pics.
4. I desperately needed an upgrade on my phone (I was using a Nokia N82. Yes, you read the correctly, Nokia N82 from when the first iPhone came out) and I thought, why not get the latest device?