As a long time float tuber before becoming a stealhead addict and moving to the PNW, I'll offer my $0.02 worth.
pontoon boats can cover more water. That is they can move from one area to another by the use of oars with less effort. And you sit higher out of the water so you have a better casting position. The down side of pontoon boats is: first of all, because you are up out of the water, you get blown around by the wind more than a float tube. And you have oars and foot rests and a whole lot of stuff getting in your way.
Float tubes, on the other hand, have none of that garbage getting in the way. However, since you sit lower in the water and you are now a dispalcement vehicle. Moving from one place to another requuires more effort,,,,and time. And because your butt is down in the water, your casting position is compromised. BUt, you are able to move short distances better by using your fins.
Everything is a compromise. What I have found to be the best of both worlds is a U-Boat style float tube with the addition of a 2 inch thick piece of really high density closed cell foam cut to fit the seat of the tube. this accomplishes several things. It raises your casting position. It raises your butt out of the water, but not so high that you get blown around by the wind. Because the foam is rigid, you now have a plaining surface rather than a displacement surface so moving about is more efficient.
Fat Cat type boats are not bad, but I prefer the modified U-Boat mentioned above.