Mark I all the way--it has the most character (italics =, flat S, spiky crown, long tail "f", and more). After that, I'd take MK III, since at least some of the rakish serifs reappeared that the MK I had.
MK II bores the crap out of me with its ho-hum safe detailing and "fetal alcohol syndrome" spacing on the Oyster Perpetual Date legend, but obviously this issue is purely "in the eye of the beholder".
