Well, assuming that both are good, never a sure thing on Craigslist, you will happier at night and around the camp with the small one.
Its quieter, easier to handle, and just less intrusive.
But, its weak. It will charge your battery, run a small TV and some lights, but thats about it.
A camper style refrigerator will work, but a compressor type would tax it if you have anything else running.
And forget most camper top air conditioners.
You only have about 14 amps running with about 18 amps surge to work with. As long as you know and are fine with the limitations going in, it would be fine.
You would hate the big one until you needed it for something. Its going to be louder, harder to handle, and a pain to work with unless you rig up something in advance. Some way to lift it into the truck or a mount of some kind.
You would need to invest in a good really heavy power cord so that the genset can positioned away from the camper due to noise.
But, with over 50 amps continuous and about 70 surge, you can have much more comfortable and less restricted lifestyle.
If you like really getting away from it all, making do with what you have, and won't miss a lot of the comforts of home, go with the little one.
But, if you like airconditioning, cold beer, and 110 volt lights and roughing it gently, and don't mind putting up with the weight, go big.
Remember, a small block will get you there, but a big block will get you there in style. But with worse gas mileage.
The wheels on the big one are just for moving it around. But, you might rig up a trailer for it or modify the existing frame to make it towable.
A trailer in which it could ride with its tires still on would be ideal. You could pull up to where you are going to camp, if its late you could crank it right where it is until you got ready for bed.
Then the next morning roll it off the trailer and roll it to where its going to be for a while.
Plus you can play around with the muffler and improve it.
At my old hunting camp, we had a big genset. We put it a ways from the camp, but we also had a fitting welded to the output of the muffler.
We would dig a deep hole with a post hole digger, attach a pipe to the muffler and stick it down into the hole so the sound was about 4 feet under ground.
Very quiet.