I have a 2 kw Honda eu2000i. It will run almost everything in the TT except the AC. We do have to be a bit careful not to run multiple high useage appliances at the same time but otherwise, the unit is fine for our needs.
We just carry it in the back of the pickup truck and then chain it to the TT frame or a tree when in camp.
On brand, I only recommend the Hondas or Yamahas because of their high reliablitly, durability, and low noise factor. Any genset that is noisy or annoying at 50 feet or more is not appropriate for campground use IMHO. Gotta be kind to the neighbors.
You can buy lots less expensive generators, but you may not be happy with them a few years down the line.
On size... Your generator guy isn't wrong if you really need to use all your appliances at the same time; 4.5 to 6 kw will do it. But there is a cost factor to consider. The Honda 2 kw that I have retails between $900 and $1,000. The Honda 3 kw is nearly $2,000. Beyond that, I don't know the pricing, but expect it to be about $1,000 more for each step beyond 3 kw.
Yamahas are priced much the same, but they offer a 2.6 kw model for about $1,300 or so. This is enough to get the AC running without damaging the unit. It's not the constant draw of the AC that's the problem, it is the initial surge to get it going that defeats the 2 kw models.
Some other considerations: The Honda 2 kw is about 50# and easily moved about by me or my wife although I get the task of lifting it up into the truck. 3 kw generators and larger are much heavier, and require wheels.
Whatever you do, buy a generator that provides clean power for computers and other high-tech electronics. It'll say so right in the specs. If it doesn't say so, it probably does not generate clean enough power for these devices.
We camp at least 30 days a year in NY State Park campgrounds where there are no hookups. Most of the campers we see there are using either the Honda or Yamaha 1 or 2 kw models. I expect to see the Yamaha 2.6 kw models begin to appear this coming season. Most of the folks we talk to cite the lower cost, extremely low noise factor, and the durability and reputation of these two brands as the main reason for their choices.
Food for thought.... If your budget allows for a 6 kw generator, you may be better served to buy a 2 or 2.6 kw unit and put the rest of the money into solar panels, a bank of 6 vdc batteries and a big inverter. Ask eman about that as he has that exact setup in his 2499.