Very different boats, the Supra is a LOT bigger and deeper. Very hard to compare the two for that reason.
It will ride MUCH better than the 205 in rough water.
The 205/x2 is famous for a great wake, with enough ballast, but the 21V also kicks out an incredible wake. Probably superior for wake surfing due to it's size.
Damn, tough choice. Both are damn awesome, all composite construction, lifetime hull warranties, etc.
I demo'd a 21V earlier this year, and damn it was nice having so much room. The rear compartments are huge, and the seats are so thick, etc.
You really can't go wrong either way in my opinion, but I'm sure people here will be glad to tell you different, heh.