Silicone for sure. It's hypoallergenic, lasts a long time, easy to clean. I personally prefer the 1/2" wide bands that go around the whole package. There are sizing guides online if you search for terms like 'cock ring sizing'.
Silicone here as well, though i found a package of three with one that i use to stretch and one thicker band smaller hole that i use for PUMP/Sex. I lotion mine up as that bear can really chaff if i'm not careful putting it on or trying to get it off.