Each persons preference for stiffness with be different from another, so make your own choices. Personally, since I always carry full-size hand-guns, I like a very stiff belt for the support. I do not even own subcompact guns, because I do not want to be tempted to carry them instead of a full-size handgun. I'd even be willing to try steel barrel hoops if I thought they would work.
The one is my stiffest belt, from TheBeltman.net. It is a dual-layer bull-hide belt without added stiffener. It costs $80.
At the other end of the value scale, I picked up a bunch of 5.11 gunbelts on clearance about 4 years ago for about $2 bucks apiece. They are still stiff and work fine, but the 5.11 gunbelts are known for having the finish scuff off the belt.
A mid-price point was the Dual-layer with stiffener from Daltechforce.com. This belt was $65. It is not quite as stiff as either the Beltman or the 5.11, but it still does a really good job. I wear this belt to work most days.
Another Daltechforce choice is this single-layer bullhide belt for $46. The stiffness difference is obvious. It is "OK" for an IWB holster, although it still sags. I would never wear it with an OWB. It may be sufficient for people with smaller guns.
The last Daltechforce is their "SuperBIO" belt. It is not leather, but is pretty indestructible, for $47. It is stiffer than their single layer belt, but not as stiff as their dual layer belt.
