Completely depends on what you want to use it for and how much you have to spend. I have run an Alumaweld driftboat for years but a coupla years ago bought a cheep ($320) pontoon for use on low or difficult access rivers. Liked it so much that I bought another one, used, from someone on this board so I could take a partner. Still prefer the driftboat on big waters or in winter though and you can't fish out of these low end pontoons.... transportation only. Refer to http://www.flyfishsteelhead.com/stories/raftsboats.htm for a good description of tradeoffs for different boat types.
Good luck!