Double enchantment. It took me almost 400hrs to get there, really can't believe how good it is. Does however make quite a few of the other perks redundant.
400 hours to get to 100 in enchanting? Wow, that must have been a pain :S. Im on the console, but I could never bared waiting 400 hours to get max enchanting. I allmost feel like a cheater compared to you now

. Enchanting is allmost a "must have" for all the characters I make, and after a few times it does not take long to get to 100,
My suggestion for the perk that would be the best all-rounder is the 100 extra carrying capacity from the pickpocket tree. Though it does not come free, by being bound to spend three perk points to get that perk and unlock it, and have 50 in pickpocketing (which is easy to reach).