I think the mistral joker rated the highest for being a pure freestyle board, and not detuned for freeride/waves.
In Fact, a bit of wave habilities in freestyle board for advance freestyle tricks is needed, a lot of advance move is started by carving hard. In another hand, a good freestyle board will do a great freeride board if you put a bigger fin(some company as JP offer quite a big fin as stock fin), those board are usually superfast and plan quickly.
Freestyle Wave board are not that good in freestyle..specially a guy like me who just do basic move(vulcan, spock, willy...), the Quatro FSW is a good one..the tail of the board is thick and slide easily, but board like JP FSW..no rocker, no kick in the tail and a kind'a pin tail very slim...catch moste of the time if you don't land it properly.
THe freesex was a great board for spock, willy etc...if I remember it right!? FOr your son, make sure you have the right volume for him, if he is ligth...go with less volume, freestyle is done best when you can pop the board without chop.
That's my 2 cents on the subject.
nord_roi