I myself prefer longer campaigns. Id have to say my favorite one so far would have to be the a modded campaign called The slot. (uses the air cobra. P39.)
Has a vary good story line, just the briefings kept me doing missions.
I also like some of the fun campaigns out there, there is a good one called ba$tards of the slot, it isn't a serious campaign, it combines some good, some and some crap planes, massive air battles with pre WW2 planes, air pirates.
ect....