Would probably still be Zero due to how annoying I found his missions to be. Although I liked the final mission for his shop, that one was actually fun. But for over 7 years he was the boss of my most loathed mission of them all - Supply Lines. I often wondered why Carl didn't just go Grove Street on Berkly or Zero and end the damn feud between the two with a gun. I mean he did that to pretty much everyone else in the game, so why couldn't he just save himself the frustration of Zero's stupid antics and just kill one of them? Humph.
I must say that I agree with you here absolutely 100%. Not to mention Zero's whiny voice every time you failed Supply Lines, which is still often for most players no matter how many playthroughs they have done of the game.