In my airguns, which are all FX, JSB and NSA are a tie. JSB .25.39's MKII's are lights out and JSB MKII's in 33.49 are as well. I have also had great success in a Maverick Sniper .22cal with NSA 20.3's in .217. I almost forgot in Maverick Sniper 25cal NSA 29.5's between 980-1000 are very impressive as well. I just got a Avenger-X in .22cal so doing testing on it right now with slugs. Trying out a NSA .216 17.5 grain this weekend for the Avenger-X as the .217's in 17.5 were a definite no go as well as the 20.3's in .217. The reason I'm trying the 17.5's is so that I don't have to increase the reg pressure from 2100psi. Reason being is that it shoots JSB 18.13's and JTS 22.07 grain pellets so well I hate to change.
Anyhow I think NSA makes a slug for just about every airgun out there.