You know what they say about boat owners - their happiest days are the day they buy their boat, and the day they sell it! I'd definitely go with the pool, although I've never owned either (pool is under construction right now).

I don't know if you live right by the water, but it would seem to me that it would start to become a pain towing the boat to the water, and packing everyone in the car just to go for a boat ride. If you rent a slip by the water, then there's the added expense for that.

Good luck! I'm sure you'll be happy with whichever decision you go with!