It's probably UFC Undisputed but I must say that EA UFC 3 has become a really good game. When it came out there were a lot of problems with it, missing content, bugs, weird movesets, but they've patched and updated it a lot and I really enjoy it.
If only the career and creator mode were better.
I'll probably wait with EA UFC 4 until it's been out a while because it has been this way with all EA UFC games. Game comes out, it's pretty shit when it comes to gameplay with bugs and moveset issues, lots of complaints from fans. Creators work on a lot of patches and updates and the year before the next one comes out, it's finally a good finished product.
So I'll keep on enjoying 3 until 4 has been fixed in about 1,5 years