Well usually operation whiteout takes a while because you can't see anything when the storm sets in and hammerhead is usually a camp fest for snipers as well as flying tanks that handle like crap which adds to the challenge. Though I have to say, I love both maps.
Actually Whiteout has to be my favorite map simply because it has a bomber that you get to from a frozen submarine and that you can pick up an icicle and use it as your knife.