Too many things to consider. Tube Dude did a great job of covering the important points. I wanted to add a few observations/ problems I’ve encountered with having both.
With a float tube, you are usually at least waist deep in water. There are others that raise you up so only your rear is in the water. I usually get wet up to my navel, and my fly vest gets soaked as it leeches up. I usually don’t have enough room in the side pockets to carry everything I like to have.
Because of being in the water, I usually need neoprene waders. In the early spring and winter it can get very painful for your toes. Some days I can only handle being in the water 1 hr. and then I have to start holding my feet out of the water to warm them up.
Float tubes are deathly slow. I recommend getting a u-tube or v-tube so you can move a little faster. If you get blown across the lake, you may have to get out and walk back, as kicking back against the wind with fins could take hours. “Trolling” can also be very tiring on your legs if you want to do it at a decent pace.
When I have backpacked into the Uintas and Boulders, it was best to have the smallest, simplest, least-decked-out, lightest-weight tube I could find. However, in most other situations, the opposite is best (if only have 1 tube). Also, DON’T choose the bicycle pump/inner tube type, as they take a very, very long time to pump up by hand and wear out the pumps in a hurry.
Pontoons are the far nicer way to fish. I use it most all of the time, except for hike-ins. You are out of the water except for kicking, where just your feet or maybe calves are in. I use breatheable waders or none at all.
You are riding high on the water, with less resisitance against the water than a float tube, and so you move faster. It takes minimal effort to troll vs hard kicking in a tube. You can travel far greater distances in litte time. (Learning to oar straight can be a pain at first.) This reduced resistance means however, that the wind really blows you around vs a tube. In faster winds I get off the water.
Pontoons are bigger and heavier. I don’t think it is timely to put the pontoon away every time I use it. I usually leave the 'toons partially inflated and partially take apart the metal bars. However, if you only have a car, I doubt that you will fit it in without completely tearing it all apart, and then you may still have problems fitting it in (not even including a trolling motor, battery, anchor, etc.).
My pontoon was about 4 - 5 times more money than the float tube.
If you have the space and money, get the pontoon. Actually, if you have the money, get both. =)