I like watching all 3 bowl.
Hauritz is capable of bowling beautifully, a really nice classical offspinner. Not a world-beater but a bit underrated imho.
Harris looks so entirely unthreatening, but that is his secret weapon. That and the toxic mind-waves that he emits to lure batsmen into crazy errors against his bowling.
Admittedly it's not saying much, but Swann is by a distance the best English spinner I've seen for a while. He can sometimes get a fair amount of turn, but has a very good delivery that goes straight on (occasionally with a bit of arm-ball swing) and his record against lefties is outstanding.
All 3 are also handy with the bat, but Swann is the best of them.