I like Engineer the best as the UMP has been my favorite gun in both
Bad Company games.
Assault - M16 with 4x scope/magnum ammo
Engineer - UMP45 or AKS-74u with extra ammo/more explosive damage
Medic - M60 with 4x scope and magnum ammo (for now until they nerf it)
XM8LMG
Recon - GOL with extra ammo/more explosive damage (I always run out of pistol ammo without extra ammo and tanks can't really escape mortars with the explosive thing on.)
G3 if I feel like actually attacking crates and capture points.
Also, that video I posted above does not seem to play the 2nd half.