Owned White Water for 17 years and on about my fourth BSD and owned one most of the past 16 years . Both all time classics and top ten games for me. White Water has more of everything...more strategy, more shots, more flow, more flippers, more depth. But it also will cost more money.
White Water is the better game, but BSD is the better bargain. You cannot go wrong either way. Get which ever one you get a good deal on first.