I'd just pick one that works for the most classes you like at once. I started out leveling alchemy to make dyes for my LS but due to how quickly weapons originally degraded, I took up woodworking ti repair my CNJ staves. I ended up leveling and liking archer a lot so I lucked out. And now once I get a few more levels I'll be able to go obsessive with materia on my staves and bows.

I guess you could also do it that way... see what gear you want to pimp out the most and level the class that will allow you to do that. That way no one has to feel bad at a failure and you don't have to worry about people running off with multiple-materia gear.

Just go and try to socialize with as many crafters as possible when you need materia set, you're bound to find a reliable one.