July 28, 2013 1:21 AM EDT
Most: Tie between Whiterun (duh) and Falkreath - I clear a lot of dungeons in that area and keep sell-punch-selling my stuff to Lod and Gray Pine Goods. Not to mention Dark Brotherhood.
Honorable mention: Dawnstar and its magical invisible bank, and thief-populated Riften.
Least: WINTERHOLD. Between there being snow, mages that glow, and nowhere to go, eff no.