My Soul, partly because it's my only good bike but mainly because it does everything I want it to do. Right now it's rigid forked and just shy of 23lbs for snow XC goodness and commuting, last year it had revs and a gravity dropper and went down the fort william DH course. Never feels like too much or too little bike, just spot on for me.
(it's my only good bike, but only because it makes everything else I ride feel a bit daft, I have a perfectly good GT Idrive 5 in the garage which I've ridden twice because every single ride, I'd sooner ride the Soul)
I have a soft spot for my Revolution Courier as well, it's a proper old fashioned bike, tough and practical and looks like it was built in a shed.