Onan makes 20 MEGAWATT generators. I prefer KATO and LIMA but that's a whole different ballgame.
Every LAST Generac I sold developed generator problems. Get bit fourteen or nineteen times and it tends to make a person Gun Shy. In short, the comebacks ate any profit involved then went after my wallet.
I paid $2,200 in 1982 for a Kato 12-turn 12.5 KW alternator (without reg). Best money I've ever spent on a generator. But now Kato makes only huge units.
RE: My opinion on Onan versus generac. Too little info here to assess the two's lifespan. Someone who owns a generac or Onan for a mere three thousand hours of use is not an "expert" on durability. Check the WEIGHT difference between the two gen sets. If the Generac turns out to be substantially lighter, it ain't because they use helium in the metal.