Depends entirely on which class ends up looking the best to me. So far I'm liking the Engineer's whole fiery napalm b****slap heavy melee and new class exclusive, the second-but-stationary Combat Drone (can't get enough skills that distract protected enemies and act as, essentially, additional squadmates).
That or Sentinel, because (A) i actually like the scissor-me-timbers heavy melee attack since it just fits the class so well to me and (

Amplification sounds like it has potential for some exponential fun-increasing by allowing me to combine my caster and assault Sentinels from ME2 and just run up on enemies flinging powers left and right.
Just waiting to see what my other two favorite classes have in store for them. CQC Infiltrator was probably my overall favorite in ME2 and Vanguard has a ton of potential with Charge being so awesome. Can't wait to see their new powers and melee animations.