I have a 19K Onan unit. It is out by the shed in its own building. I have to start it manually (diesel) but the transfer switch setup does the whole farm. I haven't ever overloaded it. I got a new HVAC unit and they told me to flip the breaker on it. It has a DC blower and if I run it on generator power it voids the 10 year warranty. I just use about 4 space heaters.
Not sure on the brands, but I had a Generac RV unit. It was a pain. Leaked oil after just a few hours. Support for them is limited as well. I would avoid one of those if it were me.
Check your water heater and furnace to see if they will run OK on generator power.