Drifblim is a "bulky" mixed attacker with decent Ghost STAB moves, but lacks any real Flying moves besides Fly, Acrobatics, and Air Slash from a transfer. It's main problem is that it has almost no coverage. Of course it has ghost coverage, but nothing else. If you were to run a gimmicky set with Weather Ball and Rain Dance (which would be a pain in game, since you have to breed and eggs and bleh), you would have Ice and Rock coverage.
Hawlucha, on the other hand, is pretty amazing. Thunder Punch, Throat Chop, Rock Tomb, and Iron Head are all good coverage options, combined with a high speed and high attack stat. Even if you lock off breeding, Hawlucha still has some pretty sweet moves and access to Flying Press.
In general, Hawlucha is better, in-game and competitively, unless you want a Ghost-type Blissey. And yes, STAB and coverage do matter in the games, unlike what some people think.