So I've seen a lot of 'god' equipment, but what i see is mostly is 'Let's put every enchant we can on everything' without regard to repairability. I don't do pvp, so I'm just seeing this from a mechanics standpoint
For example, a bow with all 5 possible enchants. Power 5 (useful), Punch 2 (mostly useful), Flame (mostly useful), Infinity (could be ignored, see below), and unbreaking3 (arguably wasteful). If we put everything in it, the base repair value for the bow is a whopping 52 levels plus whatever it'd take to repair it. So after you took so much effort to make, your bow will be one use and when it eventually breaks (after about a thousand uses thanks to unbreaking) you'd have to start again from zero. Even then, if you use it and you lose it to someone else all the effort would be in vain.
For infinity, you need to carry at least one arrow and if carry one you can carry a full stack. With a skelly farm, arrows are practically infinite themselves so it's not too much of a problem. Besides, in a normal encounter i suppose you wont be using a stack of arrows in one go. Just taking infinity from a bow will drop the base value by 13 levels, bringing it down to 39 levels (still too costly).
To drop it further down, let's take a look at unbreak3. If we take it completely, it'd drop another 16 levels dropping the base value to 23 leaving a full bow repair for about 27 levels, a somewhat ok amount. But, for a use amount equal to the whole unbreak 3 it'd take 27*3+12(for repair penalties) for a 101 levels in three sessions. If you name it, it'd take 108-135 levels, but further repairs would be cheaper (But if you logout with it in inventory it'd lose it's name wasting levels). I'm not sure, but this might be less than the cost for making a new 'god' bow.
TL;DR: A Pow5, Flame1, Punch2 might be better that the full equip. Not sure yet.
I don't know the most used enchants for armor, but i think that two prot4, one proj.prot4, and one fire prot.4 with two pieces with thorns3 are a good setup. Problem is, thorns is very expensive to repair and mixing it with non-vainilla protection is very costly for repairs.
As I read on the wiki (haven't tested it myself) Unbreaking enchants on armor have diminishing returns the more powerful the enchant. So an unbreak3 will last only about 25% more than an unbreak1. If you are going to put unbreaking on armor, it might be a good idea to use unbreak1 unless it's the thorns one where it will render your armor
A sharpness5, knockback2, flame2 has 23 levels base value. adding unbreak3 will push it to 39.
Not much else for now,
Thanks for reading!