The urethane bladder type is easy to inflate by hand or mouth, this is the "light" type mentioned. On the other hand, the cheaper ones using the truck tire innertube require an electic pump or a gas station pump to fill. The former is much better suited to going to areas off the beaten path.
Secondarily, the "U boat" type, i.e. one with a bladder in a U shape is easier to handle. Its also a lot safer to get in and out off. If you fall over at the edge of the lake whilst launching in your chartreuse and pink fruit loop (circle type), you could concievably drown, unable to right yourself or hooked up in some way.
I urge anyone fishing from a tube to carry (in an easy to get to position) a serrated-edge, one-hand-opening pocket knife. These knives are designed to cut nylon straps. A life saver. Trust me on this one, been there, done that.
Also, when purchasing your tube and fins, ensure you buy straps that will secure the fins to your ankle. This will decrease the chance of loosing a fin and going in circles all day. By the way, if you are in a circle type tube, you won't be able to tighten (and they will loosen up) or reattach your fins, so this is another reason to spend the extra 20 bucks on a U boat.
Tubing is a blast. Enjoy
Frank "The Oracle of the Coracle" Reid