1. The pink velcro strap was the worst of the 3. It costs 9.95, and is basically a peice of velcro you can pull around either your cock, or your cock and balls. You cannot create a good seal, and it pinches the skin when you try to get it a little tighter. Never buy this one, unless you like velcro burns.
2. The leather strap with buttons version would rank second out of the 3. It works well when looped under your balls, then buttoned above your cock. It created a fairly tight seal with the 3 button closer, but again, you couldn't create that vacuum seal were looking for. The cost was $13.95, and if you have some extra money lieing around, and love leather, this might work for you.
3. The best of the lot. Its plastic streches, and you pull it outwards and slide it down over yuor cock. Besides the hair that gets in the way (a tip.. if you love cock rings, shave your pubic hair real close) it Fits comfortably and snug around the base of your cock. This defiantly keeps the blood in your cock, and causes it to swell in size. Ladies who want a little more thickness from there man will like this one. Dont leave this on for more than 30 minutes at a time, or it could cause damage. The company claims you wont cum while wearing this, but i seem to every time. My cock was extremely sensitive after cumming, so if hes tied up, you can ask for anything! The cost was $9.95.

Good luck to all, and have a great time.