Kohler would be my first choice. A good company that has people. Who know what they are talking about.Kohler has a very good reputation in the generator field.
Cummins/Onan would be second. I don't feel the quality is had good as it used to be. Training is not what it should be. Some dealers are hard to deal with. Even the factory branches can be a pain to deal with.
Don't know much about Briggs units. But we did use Briggs engines. On our liquid feed pumps at the feed store. None of the engines made it past a year.
Don't know about Parmac. But I will check them out.
I wouldn't go near a Generac unit.Been dealing with them for over thirty years. They do have some small diesel units that are good. But service is very poor. Even if you can get them to come out. They are very picky about what they will cover under warranty.If they cover it at all.
There construction is poor.Manuals are a cheap photo copy that can be hard to read.The price of parts. Well you will need a bank loan to get most parts. One example PH-8 oil filter. At the time was a 2.98 price at the parts house. Order it from Generac 39.95. Some times some of the filters didn't get painted. Before they were put into Generac boxe's
There is another company called Power Tech. Not sure what they sell now. But used to be a good well built. Easy tpo work on umnit.