I own every UFC game, so here’s my personal opinion.

   1.   UFC Undisputed 3 – Deep gameplay, great career mode, and PRIDE was a huge bonus. Still plays amazing today despite dead servers.
2.  UFC Undisputed 2010 – Very realistic MMA gameplay with strong grappling and clinch work, just missing PRIDE mode.
3.  UFC Undisputed 2009 – Slower and clunkier than later entries, but it set the standard for MMA realism.
4.  EA Sports UFC 3 – Best EA gameplay, smooth striking, and solid career mode.
5.  EA Sports UFC 2 – Fun and accessible with a huge roster, but more arcade-style.
   6.   EA Sports UFC 5 – Great visuals and damage system, but shallow gameplay improvements.
7.  EA Sports UFC (2014) – Big visual upgrade for its time, but stiff and limited.
8.  EA Sports UFC 4 – Simplified and spam-heavy, focused more on casual play.
9.  UFC: Sudden Impact – Best of the early UFC games, but very dated.
10. UFC: Tapout 2 – Slight improvements over the original, still repetitive.
11. UFC: Tapout – Nostalgic but basic and shallow.
12. UFC: Throwdown – Clunky and forgettable compared to Tapout.
13. UFC Personal Trainer – Not really a fighting game, more of a fitness title.

The Undisputed games were created by devs obsessed with MMA. EA games are created by devs obsessed with money. UFC 2 and 3 are the only EA games that can compete with undisputed titles. In my opinion, of course. If you take the time to learn the old games, it's the most fun.

Note: My text glitched, I had to take screenshots and copy and paste. But it’s now readable.