Not sure how permanently-attached you're looking at, but I've found a MagSafe-compatible case and the
Lamicall ring to be a nice combo. It seems to have a strong hold and I like that the ring portion that you hold pivots inside of the plastic ring that attaches to the phone/case. As for card holders, I think it may just depend how many cards you want and the material - I'm currently using a
Thread wallet that I got on sale and liking it so far, but there are a ton of well-regarded MagSafe-compatible wallets besides the Apple one.
The other option that kind of fits what you're looking for would be the
MagSafe Wallet from PopSockets (not quite a ring), but it combines a grip with a card holder and allows for most any case you want.