Everybody is a "master" in their field of expertise. Then you can argue which field is more useful for the crew but I guess each one is essential, bar Brook music talent which is good but it is not fundamental, to a degree the same goes for Jinbe, the crew traveled Paradise and the New world for years yet they need an helmsmann just now.. (also Mihawk and his coffin make of every helmsman a joke). Fighter talents are essential as well so even the "sniper" Usopp even if he uses that talent very very rarely. A cook is not really essential since even if you don't eat like in a 5 star hotel you still survive (and are fine). Yet Sanji talent as a fighter is very well needed, just like Zoro. Nami and Chopper talent are important pretty much every day, same for Franky, without Robin you can't find the OP.
Luffy.. his talent as a captain.. sucks. Yet he has a gargantuan luck (also called plot power) which makes him always come out of the worst situations (which are caused often by his lack of talent as a captain). Also his fighting skills are necessary as well.