I've towed 11 years & 60,000 miles on a dolly because I liked my Vibe and it couldn't be towed 4 down. Only once did I have to park the dolly off site and I've never had a problem storing it with the MH (either using pull through sites or parking it behind the MH at back in sites). If you like to trade toads frequently or if you desire to tow different vehicles a dolly is a good alterative. Once you get use to it hook up time isn't much longer than 4 down
If you have a vehicle that can be towed 4 down and you anticipate keeping it for a long time, yes 4 down is a little easier on the knees as you get older. Generally the cost of a good dolly vs base plate and 4 down hook ups are not much different.
Dave