I used to sailin a local club on Lk Washington as a teen with a few SJ21's. Nice boat overall. As far as what is better.....that question is only one you can answer. And you have answered one, which is that there is a local club that races them. If youwant to race 1D, then get an SJ21. I built a small pram as a teen, wish I would have built an ElToro vs the GlenL 8 ball, as there was an eltoro group to race in. Not that I did not have fun with my pram, but, the racing woul dhave made it more FUN!
So your reason to go with an SJ21 vs a C21 or equal, has as much merit as any other thing some have said about other 20-22' Trailer sailers.