I highly agree with all of the above posts.

I think that for the average trainer set up on floats, flat bottom is the best way to go. They take less time to construct and are great performers. For the more scale, and higher performance planes, "V" bottom just seems to be a better fit to the plane. This has been my experience, as I had a Kadet MKII on flat bottoms and a Cloud Dancer 60 on "V" bottoms. Both planes worked out great and were a blast to fly. My Sea Cruiser II is a flat hull, and I think the performance is fantastic. I have a bud that has a very nice home made "V" bottom flying boat that was built around a Aerostar wing. He's had a lot of difficulty getting it off the water. Both have their strong points and can be really fun in the right situation. Great question.