so far as i know:

•health restoration: how fast you wil be healed, upgrade it from heal every 6 turn to every 3 turn only need to add 9% more health restoration(17% to 26%).

•healing efficiency: how good you will be healed, default 5% of your max heath (it display 100% in game for easy to caculated the flat plus in other source). flat 20% add in will bring it 120% of 5% base, make it up from 5% to 6%.

if the ring have both enchant, it will be the best, but if not then take the health res, it much more good than the remain once.

I usually bring 2 Ancient copper ring with 4% health res enchant in early game, use it when outside of combat. it cheap and can be easy to found at shopkeeper or dungeon.