Not because I don't know which is better. I'd say Big Boi is without question, but every now and then Dre comes out and kills it.
From what I've heard, it's been like this at least since ATLiens (possibly earlier).

On a generous day, I'd vote one of the last three. On most days, I'd vote one of the last two.
As much credit as Big Boi gets, he's still kind of underrated-- especially when Dre is brought up.