Onan is by no means the only generator manafacturer however they have made quite a name for themselves in the 3,000 to 10,000 watt range and they make products specifically for motor homes, they also make the Emerald line which is among the quietist generators on the market.
They are good products, however I can not say they are better than oh, say, Genrac or ___<insert any decent brand>___ . Others may have more input there.
I know mine works well, but then it's only a year old. At the office where I used to work we had a lovely Chevy Big Block V-8 with a natural gas carbarator and a Genrac "Transmission" It too worked well.
Having read more than a few owner's manuals, I suggest exercising the generators from time to time. If you do a lot of traveling in your Motor Home and you use the generator to run the AC, and stuff while driving, That's exercise enough. If you park it for oh, say 8 months a year,,,, That is not exercise enough, Note: These are extreme examples, I like to run mine at least every other month, Prefer every month