My field has no utilities, so I've set everything up to run off of generators. Over the years I've purchased five generators and had varying success.
I have two Coleman generators--one is an older model and has performed for several years without anything more than oil and filter changes. The other has been problematic--cheap guards that tear from vibration, pull cords that fray and break, bad piston rings, hard to start..the list goes on and on.
I also purchased a contractor grade Porter Cable that has worked pretty well. However, I had nothing but problems when I took it in for service. The Porter Cable service department had it for four months and had trouble sourcing parts for it because it used an older Briggs and Stratton engine.
My WEN generator has surprised me. I bought it from Menards and didn't expect it to last more than a year. It has over 1200 hours on it and is still reliable. Like the Coleman, we've had some of the guards tear from vibration and the power switch has been replaced twice. Still, I've gotten more than I expected out of it, considering I only paid $400 for it.
This year I finally broke down and bought a bigger Generac generator. It cost quite a bit more than the others, but after my experiences with cheaper generators I felt it was worth the money. The generator has close to 400 hours on it and I haven't had a single issue with it.
Here are my general thoughts when buying a generator for a paintball field.
First and foremost, get one that has an electric start. Pull cords break and they always seem to do it at the worst time. If you don't get one with an electric start, buy a spare pull start assembly and keep it handy. Sooner or later you're going to need it.
If you don't have any power for your field, and you plan to use the generator for more than just powering the occasional power tool, get at least a 5000 watt generator. Once you have access to power, you'll start using it to run all sorts of things at your field. My biggest generator is 8000 watts (10,000 starting watts) and we use it to run a fridge, a PA system, and it also powers an air conditioned shipping container. There's still enough capacity for it to run a 5 CFM compressor. I also wired up my registration booth with an electrical box and socket for the generator.