I have one of all of them, and I do have them all. I kept them thinking a balance change could allow them to be useful, but since that's no longer going to happen...it might be time for a purge. There are a few that I'll never use simply because I don't like the skill, regardless of how good it may be considered by some. It's also nice to know that if I go experimenting I've got a ring for that. As previously mentioned, you have plenty of inventory space to keep them all. It's kind of the same with weapons...I have a slew of daggers...but I only really use 4 different ones, same with staves, only use 1, maybe 2. Must...clear out...inventory! 
Usually, you'll only have space for one on your character, although there are situations you could use both slots. I have 2 of all the Superb Rings, but rarely use anything but HOK & Crit Damage. I figure that once you settle on your primary builds for each character and how you like to play them, your answer will become clear.