Best generator? What size generator is needed?

It all depends on what you want to run at once and how much you want to spend.

See if this article helps:

That said, when I’m boondocking, my goal is to run the generator as little as possible- specifically for recharging batteries and for running high watt appliances (microwave, A/C). Everything else runs off of battery power either native 12v or inverter making 120v.