I don't like the smaller Generac units for a number of reasons.
First, the quality of the "pre-packaged" ATS switchgear doesn't exactly inspire condfidence, and doesn't allow for much flexibility, like excercise times, automatic excercise with transfer, and so forth. (If you're not excercising with transfer, you're wasting your time.) I would much rather have a genset with a two-wire start that can be used with a more "substantial" ATS of my choice. Plus switched neutrals if required by local code are almost impossible with lower end Generac's.
Second, up until recently, you needed very high (11-14" WC) natural gas pressure to run these units, though now they can run on (5-7" WC). Onan is much more flexible, usually allowing 7" to 15" WC, though many can run with less without any problem.
And finally, I've found these units can be very finicky to get going, and there's often insufficient space to make connections. I don't like the idea of attaching a NEMA 3R box outside of these things simply to reduce the conductor size so the genset can accept them. Annoying. And it seems too many of these units come DOA, and need parts replacement. Never seen and Onan or Kohler come DOA.
Now when you get into the bigger Generac's, like 100KW and up... those can be pretty impressive, both with the genset and ATS switchgear. Those tubrocharged CAT engines are a sight to behold. I really don't like the consumer grade stuff.
I personally like Onan - have one myself - but I am very impressed with the new Briggs & Stratton units and their load management controls. B&S will soon be shipping their new EM20 genset, a 20KW air cooled unit with 28KW surge capacity that can manage TWO 5-ton central A/C units with the Empower controller. And I guess I like B&S because I could work on those motors as a kid, and they're pretty darn reliable. But of course, the motor is only half the equation in a genset.
I'd want it to back up my house for whatever period it needed. I wouldn't run it 24/7, I can get by without at times. I'd like it to run my deep well pump, freezer and maybe furnace( I can easily heat my house with wood though). Wesco Distribution has 10 of them and its tempting. I already own a 3000 watt Onan, its been very reliable but its not quite big enough.
Generac provides poorly for the end customer and does not take care of the EC dealers.
If a homeowner calls Generac with any question or concern they are given the EC phone number in place of a help customer service.
A dealer must fax written orders on anything as small as an oil filter. At least some items are not returnable.
A dealer is sold a required service parts kit. I believe the perferd dealer needs to buy more parts, have an 800 phone number, and provide 24 hour service.
A dealer needs to provide warrenty service reguardless where the customer purchased it or who installed it.
For warrenty the dealer may need an authoration, purchase parts from Generac, do the labor, send in the paper work maybe old parts, let them check the old parts and paper work, then they will give you a credit. Next you need to call the credit department to get a check sent to you. It can take 8 weeks to get paid a fixed book amount for a repair.
To repair them you need your metric tools, extensions, swivels, and many auto mechanics tools.
You can be on hold for an hour to get someone from the parts department. I never got any catologs where I could just look up my own part #, price, or even see if I had the correct part in stock.
They have been inconcistant on the gas pressure requirments.
The tec support provided the wrong information more than once. Things like the cut sheet on where to put your pipes in the cement pad.
The models change faster than they can update the information for them. I Ordered one liquid cooled that was the newest model. By the time I got it way latter than promised it was allready discontinued.
The sales rep never lasts for more then a few months. They will call you every week to let you know on the latest deal like buy 10 units now and get 3% off.
I been told a few times by a potential customer they claim things on the Generac web site like air cooled units are priced from (not much more then I pay) and can be installed in a few hours.
The home centers sell the same units for a little more than what I pay for it from Generac but do not proved warrenty work.