You need to give more info for us to help you.
How aggresive do you plan on being
Only rivers, just playparks or play your way downriver
How willing are you to work at learning
Any paddling background ie: canoe, seakayak...
How much are you willing to spend
so on and so on
The bigger the boat the more stable the smaller the more playfull.
The new bigger boats you won't grow out ofas much as grow into them by running bigger water, steeper grades and such.
A riverplayer is a little harder to learn in but it will help you learn the skills you need to handle bigger water.
Depending on your focus and size...
All good riverrunners surfer/players
Never paddled other brands of that type.
Liquid Logic Lil Joe/Hoss
Good riverrunner/bigger water boats that will surf too.
Also check out http://groups.yahoo.com/group/Coloradokayakers/
there are alot of newer paddlers there to play with.