I agree with Jeff; some clue as to the budget would be most helpful. Along with that, are you looking at new or used motorhomes?
Especially if used, a good deal of what you're likely to be looking at will be based on the Ford E series chassis and probably have the V10 engine. It's a decent enough chassis, if somewhat dated in suspension and overall design--generally quite reliable and not terrible to work on and with good support for parts and aftermarket bits (as ford sold zillions of E series vans and chassis). Tow ratings vary somewhat with the RV maker and what hitch they install and how they install it, but typically max out at 5000 pounds, 7500 pounds for the newer E450's. Tongue weight is frequently more limited, which is not a particular concern for towing four down or with a tow dolly since the weight is pretty much fully self-supported.
Personally, for shopping used, I'd pay a little attention to the manufacturer and more attention to the quality of maintenance the previous owner(s) have used.