RAM doesn't affect performance unless you have too little. Even the Nexus 7 has 1GB of RAM. The 2GB is there just because they were making up for swapping out the processors. As an i9300 owner, I'll say this: The One X looks and feels better, but it's nothing a case can't take care of. Now, between the One XL and the S3, I'd choose the S3 for a few important reasons:
1. One XL only has like 9GB of usable storage. No memory card slot.
2. No removable battery - if you swap batteries or just wanna replace it after two years, you can't.
3. ROMs - You need to give your IMEI to HTC to get a partial bootloader unlock, and it voids your warranty.