What vendors sell better mods and enhancements??? You craft blues (and purples if you really want) , but I have only seen vendors sell green quality.
IMO, Cybertech is probably a good choice, but Armstech will allow you to build blaster barrels, so that is pretty darned useful.
I have a stable of alts with all the crafting skills, so I make what I need when I need it. I have sets of legacy bound armor set up that I pass around as toons level up.