Personally I think it's Spark Brushel (4th case of Apollo Justice). He pisses me off to no end, also Wocky Kitaki is pretty annoying but nothing can compare to the annoyance I feel when I see Brushel, He is the worst and most annoying charcter out of all the games. for those of you wondering what he looks like here is a picture.
http://www.court-records.net/chara4-4.htm#hamigaki
So who do you think is the worst Phoenix Wright/Apollo Justice character?

Wocky, Winston Payne, Brushel, Larry sometimes, Dahlia, and probably a couple more people really bug me in those games.

Mya, Wocky, Winston Payne, young Edgeworth's clothes (T&T, case 4--I think), Larry & Daryan. (so far--I haven't finished AJ yet)