Enchants are easiest to manage by abusing pyrite on gregtech > In about an hours work of farming you could get yourself full best possible enchants by using pure enchanting + an anvil to combine them.
Twilight enchants are weak, mostly because the armor is weak. The wiki says that steeleaf is comparable to diamond without the durability, but that is definitely not true. Fiery also is not equivalent to diamond in either strength, speed, or durability. The fiery sword is the only fiery piece worth considering, ever. That's simply because it's the cheapest sword you can make compared to nano's EU cost and diamonds use for other things - assuming you've killed a hydra or two.
Hands down gravitation suit, ultimate solar helmet, and the other quantum pieces win, but if you are on gregtech these will take a long, long time to acquire. In the mean time quantum is actually extremely weak if you aren't using the chest (using a jetpack, batpack, etc.). I wouldn't even bother making these pieces until you are near/made the gravitation suit and preferably the helmet too, as even nano will work if you need 100% damage reduction and enchanted diamond gives 96%.
Longfall boots are handsdown the best thing you can get early game, but once you hit midgame - it may not always be perfect. If you are using a jetpack or batpack, you will get more overall protection from enchanted diamonds boots (to compliment the armor)
If you are as mentioned numerous times before in this post, using some form of armor that is outside of the quantum set, the rest of the armor should be diamond. This includes when you use longfall boots really.
Enchanted armor (I say diamond simply because of it's strength and durability, but any will work - ironbark is easy to get strong enchants on without an enchanting table), will give an 80% damage reduction to all forms of damage except falling. This means that it will beat the 50~% you get from quantum without the chest, or the 75~% you get without the helmet, because you will also get protection to damage from the armor itself. In full diamond this is about 96%, without the chest it's about 88%. To reach this plateau you need Protection IV, Protection III, Protection III or greater.
I wouldn't bother repairing enchanted tools on an anvil, it's extremely expensive. The only possible exception I personally make is bows and swords - for infinity + power, and looting III. Tool enchants are easy to come by (and honestly unnecessary on anything except a pick - I still prefer a mining laser for general purpose). Looting is a great enchant for getting ender pearls, blaze rods, shorter with wither skull grinds, etc.