It'll depend on the class. Each weapon type basically has one "primary" crafter for it, though some weapons are on other ones (the bluespirit level 74 weapons having almost half under GSM immediately springs to mind).

BSM gets the most weapons, being the primary crafter for all tanks, SAM, NIN, DNC, MCH, and a decent chunk of MNK

ARM handles PLD shields

GSM handles RDM, AST, and an assortment of BLM and MNK

ALC handles SCH/SMN books, most BLM rods, and a few WHM staves

CRP handles DRG, BRD, and most of the WHM staves.