As infrequently as you tow, I would say that you would be better off with a half-ton for a couple of reasons. First, when you are not towing, the half-ton will always be more fuel-efficient. Second, F-150, Silverado 1500 and Ram 1500 all have a car-like, next-gen suspension. The 3/4-tons have a tighter, stronger suspension for increased payload. They are naturally going to be bouncier when there is no trailer on the hitch. Finally, if you've been to an RV show lately, you will notice that there is a trend to design for half-ton towing. Keystone and Forest River both have 33-foot bunk-house, rear-living room and rear kitchen models with a tounge weight under 700, and dry-weight under 7k.
I have a neighbor who is a real gear-head, and he has the 2500 version of my truck. He said he wished he got the 1500 just because of the suspension. (To be fair, he doesn't tow a TT)
It's all very subjective, but if you ask me, the HD's are for the less-than-casual-rv-er or a fiver-driver. :)