Best Cock Ring

If your guy is a beginner - start with a simple 2" silicone ring. But once he gets the hang of that, he may want to try steel - check out my review for the Omega link

I'm assuming that this would be his first c-ring, so you'll probably want to stay away from the less compliant materials like metal for the time being. The most important thing to consider with a c-ring is the fit. Too constricting, it could be painful (unless that's what your going for). Too loose, it defeats the point of having it on in the first place.
In my experience, the super stretchy jelly ones tend to be comfortable, but because they are super stretchy they provide little to no constriction, thus becoming more decorative than functional.
The silicone c-rings, like the one you have shown, tend to be a popular choice for starting out. They have some stretch but are still able to provide constriction of the blood flow. Hope that helps.

I agree that if this is your first experience with a cock ring, you should go with something flexible. This ring, Beginner Cock Ring, is a great starter ring. It is silicone and pretty stretchy. Measure first to make sure you get the right size. I put measuring instructions in my review of the Barbed Wire.

I agree with Gunsmoke and Kissaki that the Omega is THE best cock ring available, but it isn't one you want to try first. As we've all said, try the silicone first, and get him used to wearing one. Then move to metal.
The Omega is like moving from one extreme to the other. It's the heaviest one I've found. Worth every penny, but may be too much too soon.

Get him used to wearing one, and work your way up to it. You won't be disappointed.

Thank you all so much for the help. It's a daunting task when you have no idea about these things, but he's the one that wants to try one, but is leaving it up to me to do all the research. I really needed a guy's perspective and I really appreciate it so much. You all are GREAT Thanks.

Oh... this my likely cock ring too)