Holy ancient thread, batman!
My definition of "belt knife" is something that's actually comfortable to carry. That rules out my big choppers, kukris, etc, which are usually either inside a pack or lashed to the outside. In that case, I'd say my perfect belt knife right now out of the stuff I still own is a Scrap Yard Scrapper 5 LE - it's beefy enough that it can take some abuse, has a great balance due to the hidden tang handle, the mudders are super comfortable, and INFI is easy to field sharpen.
That said, I am starting to get the itch for some customs in the 5" range, and will likely be snapping up a few in the coming months, so my decision might change slightly. There are a couple minor things I am not in love with on the S5LE, but the steel and handle will be tough to beat.
Edit: forgot the pictures!
Second one down:
With some other favorite tools of the trade: