I'll post my Merc Reunion co-op scores with what character and current leaderboard placement.
Public Assembly: 735,556 - Josh (749th)
The Mines: 657,775 - Josh (318th)
Village: 728,577 - Chris (Warrior) (354th)
Ancient Ruins: 378,516 - Sheva (Business) (197th)
Experimental Facility: 431,629 - Josh (250th)
Missle Area: 326,437 - Josh (254th)
Ship Deck: 534,359 - Josh (51st)
Prison: 864,757 - Sheva (Business) (184th)
As you can see, I like Josh a lot. Would be replaced with Wesker if he was on Reunion though...
Funnily enough, i hardly play with a mic when playing, unless in a party chat or something. But I communicate a lot with the B commands. As far as tips go, collecting all the time before hand and picking when to get the combo bonus is crucial. I always pick up my partners power gun (ie. magnum/grenade rounds) ammo. A partner with ammo is much more useful then one running around trying to look for some that you could have got. And melee moves are your friends.