We went small to start with but our friends have gone the opposite route and gone steadily larger though now they are regretting their decisions with the reduced number of campgrounds they can use and the greater depreciation when it comes time to sell.
For the tow vehicle there is a knee-jerk response to tell people to get a F-550 and not worry about what they will be towing. The reality is that more than three forths of the people I see towing 5th-wheel trailers on the highway are doing so with SRW 3/4 and 1-ton trucks.
The bigger the trailer the longer it seems to sit on the market when it is being sold. I have seen some very nice ones that take a 2-ton truck to haul them around and some have been on the market for over two years and still not sold.
If we need something bigger for a particular trip we will fly to the area and rent an RV. No point in buying one and storing it and transporting it a couple thousand miles and back again for a trip of less than a month's duration.