Belts here fall into two jobs, and they are not the same purchase.
Carrying belts
If the belt is holding trousers up and nothing else, width and looks decide it. The Hoggs of Fife luxury leather and the Harkila Arvak leather are the smarter end; the Deerhunter canvas and Jack Pyke Countryman elasticated are the everyday ones. Where you are hanging a knife, a bino harness tail or a dump pouch off it, go for something rigid — an elasticated belt will roll and sag under a loaded sheath.
Cartridge belts
The Guardian Heritage and Guardian Canterbury 12g belts carry 25 loops in canvas-and-leather and chestnut leather respectively. Loops stretch with use and season, so a belt that grips new will loosen; that is normal and it is why old belts drop shells. Worth checking before a driven day rather than on the peg.
Sizing
Measure over the clothing you will actually wear it with, not over a shirt. A stalking belt worn over a smock and a fleece needs a good deal more than your trouser waist size, and European sizing on the Scandinavian brands runs in centimetres.
Related: Cartridge Bags · Hunting & Shooting Trousers · Knives · Waist Bags