When it comes to enchanting, it basically depends on your smithing perks. If you have the perk that allows you to upgrade enchanted gear, then do it however you want. If you don't have it, then smith first, and enchant after.
Essentially, enchanting before smithing, and vice versa, don't effect the outcome in the slightest. Just be forewarned that you need a perk in smithing to upgrade enchanted gear.