In detail is something you will need to read through on their websites and try to understand the differences from their individual architecture point of view.
This would turn into a very very detailed thread and a long one if we were to post the entire thing here and will really take a lot of editing time....
Just be aware that the vast majority of games only use 2 cores. There are a few games that uses 3 or 4 cores, but they are in the minority. More games will use 3 or 4 core in the near future, but they will still be in the minority.
Developing a game to use many cores is actually complex and time consuming. That also means it takes more money to develop. Current games that can use 4 cores, do not use it effectively. It's been a while, but there was an article I read back at the beginning of 2011 or late 2010 about CPU scaling in games that can use 4 cores. It showed an average of 26% performance improvement going from 2 cores to 3 cores. But just another 6% on average going from 3 cores to 4 cores.