I use to have a round tube, it was good, but the shape has some problems. The main problem is ...space... in a round boat everything is very cramp the space to put your tackle and other things is very limited and it is difficult to have rod holders or more than one rod. You don’t have very much mobility and it is far more difficult to land fish. This is why I recommend using a u or v shape float tube. And about the stability, some people say that the shape makes a lot of difference, but I found this not to be a problem. They are all as stable, except when you are in big waves, only then are a round boat more safe.