That's an interesting question, and one which my club debates endlessly.
First, we'd need to know a little more about you...how do you like to fly? What's your budget? etc. etc.
As a general rule, if it flies good on gear, it'll fly good with floats.
The caveat being, a set of good floats and hardware can easily weigh two pounds. (I'm talking about a set of Great Planes 60 sized floats, which will float a 15 pound model)
So, don't forget about wing loading.
A real nice plane to start with is the Sig Kadet LT2...I think I have all the numbers right on that...40 sized Arf trainer by sig in any event. Lots of lift, big vertical tail surface.
Our club flies float planes almost exclusively...and we have found that almost anything will fly with floats strapped to it. Below is a pic of the TTChamp45S, a 40 sized pattern platform, with 20 sized great planes floats.
Seamasters are very popular here...there are currently 5 of them in flight ready condition in our group.
Also popular is the (discontinued) Great planes trainer 60...because of it's wing...semi-semetrical and hi mounted.
I've got a profile plane on a monofloat...flys great. While it flies perfectly fine in normal flight conditions, the float brings out some strange behavior when doing aerobatics. We call it the 'pendulum effect'. Snap moves entered while inverted are MUCH more violent as the weight of the float and gear whips around. Pretty fun.
I've also seen Ventures, Tower Trainers, a TwinStar, a Telemaster, several Cub varieties, a Husky, profiles, a Lazy 51, a PT-40, an RCM Funster, and more...with floats strapped on. Just do it!