This chatter about preferring to play as character X/Y/Z seems a bit too role play-ish to me, but whatever floats your boat.
The only things that would affect my decision would be any gameplay differences. Like how Johnny and Luis had improved bike and car handling respectively, I understand Franklin will have improved road vehicle handling due to his experience as a vehicle repo man while Trevor will be best for aircraft due to his military background. Is this confirmed?
What about Michael? Guns maybe.