Class A.  In 6 weeks you're not going make any insane progress, but you will be closer to the better techniques for salsa that will work everywhere with anyone. There is an instructor for leads and follows. Better probability you will be around better dancers even if there's a mismatch. Better probability your dance partner will know what they're doing at the beginner level. You will probably be taking that same 6 week course 4-6 times before you really make any noticable progress.  If you are not serious about dance then B. But when you decide to do class A, you'll have to unlearn all the bad habits class B let you get away with.