We've had Generac 20kw auto standbys for probably 10+ years? They serve us fine. However, locally the Briggs & Stratton standbys seem to have gotten popular. Installations & service may be deciding factor. I'm guessing most of the generators will probably last longer than the people doing the install & initial service. If I was buying another tomorrow, it would be a 20kw B&S because of local dealer.

I realize it's very easy for me to spend your money. Most will suggest to add up your running watts you might need in a power outage and then buy a generator only exactly that size. I felt we might as well get the biggest affordable & not have to worry about future loads, like 20-30 yrs down the road. I assume my generator will last 50 yrs plus. Going above 20kw usually means going to liquid cooled vs the air cooled of the less 20kw & less. Liquid cool means a lot more money, though output load is almost no restriction with liquid cool. Don't forget that when the chips are down....it's usually a bad time. If there was a big storm & power is out, that usually means the sump pumps are running full blast and if it's a summer storm, so is the a/c unit. Not a problem with a 20kw unless you have something unusual.

I've had no trouble with my Generac 20kw generator. Change oil (synthetic) 1x per year. I put a new battery in after 5 years just because. Generator exercises weekly.

Good luck.

Edit to add install price. I believe my install price, including wiring & running NG pipe was less than others indicate. Probably a little over $2000 installation cost.