I've played primarily as Commando. Beat the game three times so far. Once as Gunzerker, twice as Commando. I haven't played as Mechromancer yet but plan to do so. I've only played Assassin and Siren long enough for the Trophies (although I must admit to power leveling my Assassin.) Didn't care for either class though.
If you don't have a sense of humor, you probably don't have any sense at all.