I'll give you my choice for the best first float plane and it's not on your list. The Sig Kadet /Senior on built-up/glassed floats. It flies and lands scale with no bad habits. For a first seaplane I would select the Seamaster , Mariner or a clone.
From your list:
Widgeon: I never flew one but I'd stay away from a Twin Seaplane as a first float/seaplane.
Catalina ; Nice plane but I don't think it's a good choice as a first float/seaplane.
Beaver: Never flew that model but have flown a similar sized Beaver Nice flying floatplane with no real bad habits.
Giant Stik: Can't beat a stik on floats!
1/4 Scale Cub: Watch the take-offs and landings as those little bad habits are amplified with the floats. Also the handling in the air is exaggerated...just need to be on top of it.
Actually almost any floatplane will have exaggerated handling because of the floats. Some planes handle it well others not so well.
From your list I would choose the Beaver or the Stik.