I'd agree tthat the $1900 would be the first one I'd check out. The d466e is a good enough engine at that price and with those miles. Guessing based on looks I wouldn't expect it to be geared for long highway drives, though.
If you're mostly stationary, the engine-driven ac in the Thomas isn't that useful to you. It's a fair price, but doesn't match what you've said about use. I'd look toward a cheaper bus and save the money for RV-style plug-in electric roof AC units. From the available info, this one is likely the best highway cruiser. If you're a shade-tree mechanic diy-er, I'd avoid Caterpillar engines like this one though.
Can't really tell about the other two without more info.