I rarely drink soda any more, but I always preferred Dr Pepper over Mr. Pibb. Much like Sprite and 7Up, Pibb is a little sweeter than Dr Pepper, though not as much as Sprite is over 7Up. I'll drink 7Up, but I don't like Sprite at all, way too sweet. Mr. Pibb isn't overkill like that, but I do like the slightly less sweet Dr Pepper better.
Nowadays, though, on the rare occasion I do have a soda, I opt for Barq's.