just installed the Air Dog 4G and I love it. Cant even hear if its on or not. I will say the instructions it came with were outdated and not for a 15 LML even though it said they were.
I think they're all good, some have better features than others. I went with the AD 165 about 4 years ago, never a problem, very quiet (I have to really listen every time before I start it to make sure it's running). Whatever you get, make sure it's a "flow through" pump so if it does ever quit, you can still drive it without having to replumb it.