Well, I had to say legs... as "Lats" didn't cover my enire back. I love the feeling I get when I train my legs... they can inflict the greatest pain on me...
In CLOSE second, I'd say back. Normally, I generally like to train Chest -- but it hasn't been a favorite to do with my shoulder injury... and... lol -- well, I don't like training shoulders or triceps as much as the others...
Guess that leaves Biceps and Triceps tied for 3rd.