I go with what I think is right for the character. That is, they should be able to make things they can use. I once tried having a hunter with Armourer, thinking that making the crafting tools would be useful to them, but decided later that it just wasn't them and switched to something more useful (they were 30-something and already accessed the superior forge at that point).
I try to envision what the character will be like, their personality, goals, and so forth. And then pick a crafting vocation that goes along with that. Sometimes I have it picked before I even start the character, and sometimes it takes a while to decide what they want. When I can't decide right away I usually go with Explorer to gather ores and wood until I can decide and then change it (usually happens before the starter tools wear out).
"Everyone's got one. Better to be a smart one than a dumb one." - me
"It's people like you that [I]think[/I] you know everything that give those of us that [I]do[/I] a bad name." - me
"Eat, drink, and be Merry, 'cause Pippin was a fool of a Took."