I’m of the mind to spread it out. If you’re playing an engineer you have little need for tailoring for example. So you’d have to hop on that char, pay to go back to tailoring, then make the item, then pop back to the other char to get it. So in answer to your question, I’d say just do the crafts on the chars that can use it.
Personally I love the exp rewards of crafting, I’m tempted to max out a craft on more than one char just for the exp, so I don’t have to grind up my levels as much.
Though now you have me tempted. Almost seems worth it to try and max out a char without doing quests, just crafting their way to level 80!