Noise aside (inverter generators tend to be quieter due to more sound insulation and the ability to run at low RPMs), there are three general types of generators:
1: The cheapies. These will have a motor with a shaft spinning at 3600-3800 RPM, a generator head with two poles, and a circuit breaker so the whole thing doesn't fly to pieces if overloaded. Attach a load, engine slows down, and the frequency/voltage takes a brief hit. Take a load off, get a voltage spike. I've seen on Youtube the $100 ET800 clones get up to 160 volts in a burst. Not good for anything more delicate than an incandescent light bulb.
2: The good open-framed models. These have some voltage and frequency regulation built in so it will cut the circuit off when powering down, and try to keep voltage within a reasonable range. A Champion 4000 watt is a good (although quite audible) example of this.
3: The inverter models. In general, they will product 120 volts or 0 volts, although sometimes they can overload and give fewer volts for a short time (A/C compressor locked rotor amps for example.)
I would never buy any generator model from the #1 category (which mainly consists of no name generators.) If one wants a decent open-framed model, buy a Champion. They have very good customer support, and even though their stuff comes from China, they always have parts available. Of course, for camping, the best are inverter generators.
As a rule of thumb, generators work best when they are halfway loaded, so if one runs an A/C mainly, a 3000-4000 watt model would be ideal, or two paired 2000 watt generators.