The adult size has normal plates and cheaper "leather." The deluxe uses a more realistic leather, but still has regular plates. The plates on the ultra-deluxe are twice as thick, and the belts are just about twice as heavy. They feel less like a toy and more like a real belt.
Some things to keep in mind, though - when you have belts with the thicker plates and the regular plates setting on a shelf, you don't really even notice the difference. You have to get closer to them, or better yet, hold them to really tell a difference.
Also, just because the plates are thicker doesn't mean the engraving is any deeper. That's some very important info I wish they mentioned on the sites that sell the belts. The engraving on the plates is exactly the same on all three styles, just with thinner or thicker plates. On all three types of belts (even the ones with the "better" straps), the material is simply covering a cardboard strap, and it's pretty obvious. You'd have to get the belt re-leathered to make it look and feel more authentic, and that's another $200 or so.
If you want a thicker plate with deeper engraving, they have a new style of replica belt like that for $1,000, but if you've got that much to spend, you'd might as well spring for the $2,500 the real thing costs.
The ultra-deluxe looks nice, but if you're just going to set the belt out for display and don't care if it
feels more like the real thing, by all means get a standard adult one. From across the room, you can't tell the difference.
Which belt were you thinking of getting? Some of them are only available in the standard adult style.
Average, Fat, and Really Fat?
Just to clarify though, all of the replica belts are the same size as the real thing.