There is a wide range of what can be considered a playboat. From something like the RPM to the rockstar. Depends on how fast of a playboat you want and the sort of features your river has to play on.
I recently moved from a Pyrahna Molan (pretty much a rockstar/allstar boat) to a gen 3 4fun. The added hull speed and lower volume at the ends make it a more versatile boat. It wouldn't be great for loops / big wave moves, but I'm 99% I won't be either. I'd say unless you know for sure you'll have the places to use a small playboat like the rockstar/mobius/jed/etc go for a boat that is a bit longer and faster.