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Build your own. 
10Kw, diesel powered, 1100cc 3cyl Kubota engine turning 2150 RPMs. Total cost less than $1000. It will run the entire house including the water heater and stove as long as you only run them one at a time. The 13 gallon tank will run it for longer than I have ever needed.
The only thing I would do differently is to use a ST generator head rather then the cheap HF one. The HF one hasn't failed yet, but I have had to rewire it due to crappy wiring.
Buy a diesel powered welder from craigslist and put some outlets on it. That way, you can justify having something you only really need once a decade by using it to make a tube chassis MGB-GT with LS power when the lights are on (or, hell, you can still weld when they are off!)
Champion and all the others that look just like it all universally have good ratings, and cost about $300 for 3,000kw. They seem to last for years, and fire right up after sitting there for several months or years. They just seem to work real well.
For zombies, I'd go gasoline. Even with ethanol, stored inside it lasts for years just fine. Propane is expensive to run, bulky to handle, and you can't refuel your cans with the world ends, like you can with gasoline.
Generators work great if you use extension cords and the like and plug various appliances directly into them. Life gets ugly if you foolishly try to backfeed through the panel box via outlets. Houses burn, claims get denied, power companies collect large settlements for their damaged equipment.
