Chris, A float tube like a U boat style is the best for small still waters in my opinion, the advantages are (1) they are much lighter than pontoon boats and easily carried to your fav lake, (2)very easy to operate with waders and flippers, (3)not affected by breezes.
Disadvantages: (1) You cant go very far or fast in them. (2)They are not to be used on flowing rivers very dangerous if your feet get caught on a submerged object, you can be easily capsize and drown! (3)Just after ice out, the water temperature will be cold enough to ensure that your float is very short. many layers of underwear pants what have you and breathable or neoprene waders are the answer here.
Pontoon boats.. disadvantages, (1)harder to transport to your lake, much heavier than a float tube. (2)More susceptible to wind drifting, pack an anchor with you.
Advantages... (1)can be used on either lakes or rivers, you are higher out of the water hence this gives you better vision. (2)you are warmer as you are out of the icy water, (3)Using oars or an electric motor gives you much more mobility than a float tube in the water. you can still use flippers for hands free operation... I own both a fishcat 7 pontoon boat and a fishcat 4 U boat. I use both extensively during the spring to fall season.