I voted Phoebe but now I’m thinking Joey. They both serve as an antidote to all the bougie of the other four but Joey just isn’t all that interesting by himself.
On a personal preference level, I really dislike Rachel and by extension, Jennifer Aniston. I guess that’s a credit to her acting; I don’t dislike her in other things I’ve seen. As Rachel, I’ve come to hate her face. And her voice.
Rachel, because she was the normal “pretty” one and, IMO, quite vanilla compared to the others. I think she would find a vanilla guy and disappear to be replaced by her wannabe-Broadway-actor little sister.
He and Chandler were college roommates so while he may be older, it’s probably not by much. Rachel & Monica are about 2-3 years younger with Rachel the youngest (she was the last to turn 30). They’re all within a few years of each other.