I don’t have a favourite antagonist, but I do have one that I disliked with a passion (as you should with a bad guy).
Razor from Need for Speed: Most Wanted
That douche took my car after sabotaging it in a race! What a jerk. There isn’t a bad guy that I hated as much as this dude. Ahhhhh, just thinking about it makes my blood boil! Now I want to play the game and get back my car! (even though that’s not my preferred drive, it’s the principle of the thing).