My vote would be WH2O hands down.  For me it is one of the best all time pins.  Yeah it doesn't have drop targets but it has everything else in a pin on tap.  The rules are deep enough to make Vacation Jackpot bloody hard which keeps you coming back for that one last game.  If you haven't seen the Vacation Jackpot in real life, take the glass off and give the machine a tickle, it's one of the better jackpots I have seen - just turn the machine off at the end of it so you don't save the highest score.

So why am I selling mine I hear you ask?  I love it that much I have two at the moment and sadly I can't keep both - I need the room and $$$$ for another machine.