Team leader: Ibram Gaunt from Gaunt's Ghosts. http://en.wikipedia.org/wiki/Colonel...ar_Ibram_Gaunt
Medic: Retsu Unohana from Bleach. http://bleach.wikia.com/wiki/Retsu_Unohana
Ranged support: Vash the Stampede from Trigun. http://en.wikipedia.org/wiki/Vash_the_Stampede
Melee powerhouse: Roronoa Zoro from One Piece. http://onepiece.wikia.com/wiki/Roronoa_Zoro
Melee support: Mirajane Strauss from Fairy Tail. http://fairytail.wikia.com/wiki/Mirajane_Strauss
I'm a little iffy on wether Vash counts as overpowered, but my argument is that, due to his personality and philosophies he can't be counted as overpowered.