For me those adjustable ones have not been great. I do have one and it wasn't the cheapest, but it surely is not to my liking. Usually the adjustable ones will slip and they do not do their function as well as they should.
Just my viewpoint, maybe others really like them. To me, the fit is too loose most of the time, constant adjusting and so on ...
I've favored O-ring type rings. I actually bought a big set of different sized ones, so now I can use an O-ring specifically for head training, to get that nice full "mushroom" effect.
As DLD has mentioned, these should be available pretty much around the world, most likely from an automotive shop. (Those shops are good for other PE related tools as well!)
Brand-wise I've liked Oxballs. Especially Screwballs and Powerballs. (If you google, the main website for their products is very gay.)
Slightly I'm interested in trying the Horseshoe by Hardwear cockrings (warning, if you look for the site; the content is quite gay ...), but their prices throws me off.
Best will always depend about the user. For girth, O-rings are great in my opinion. Sex, my experience is not so good, but I'd think something with a vibrator could be fun. O-rings can be a bit too restrictive for sex in my opinion, but can be used!
For all day wear a snug silicone ring with some width would be my choice. The width makes it more comfortable to wear for a longer time. Silicone or TPR. TPR isn't the best in my opinion, but manufacturer matters! For all day wear I could suggest Powerballs worn just around your cock, should be snug enough.
Could you PLEASE provide a name or link to the cock ring you're talking about. 
