We've had two Coleman Mach non-ducted A/C units. Good performance, longevity, and few problems with both. First was 25 years old when we sold the coach and it still cooled well after a good
CLEANING. It was a 13500 unit.
Our present Mach is a 15000 (think it's called Mach Plus). At 10 years old, I just had to replace the blower motor and cleaned it while I was at it.
Just from looking at RVs and reading here, I think there are somewhat more Coleman units in use, but more problems with Dometic reported here. Even if it's true, I don't think the differences are significant.
I also like the way RVP (Coleman) makes all the documentation available. Drawback I see on the 15000 Coleman A/C is I can't find a high efficiency version like they have for 13500. Sure, campground electricity usually isn't metered, but 30-Amps isn't much and reduced A/C consumption would be nice. I don't know how this works with Dometic.
And I share you opinion on Advent Brand. Availability of Parts and Service is very critical to me. RVP/RVComfort/Coleman has worked out well.