Onan 5500 EFI vs Carb.

If I was given the option of EFI vs. carb I'd take the EFI. I'd be the early adopter (early adopter EFI 2015?). For me the advantages would be less or no clogging issues and any decent implementation would have automatic altitude compensation. It should start easier when cold. Fuel economy-not much different unless the carb setting was way off for elevation.

I've had several small engine EFI systems in the last 5 years which ran flawlessly.

You're running a risk of early kinks. Fuel hose configuration is something you should check and weigh in decision.

Since my post I have found a couple of comments that perhaps the EFI requires a return fuel line to tank so if it isn't installed, I'm guessing that would mean tank drop too.

Something to chew on...

Maybe there's too few EFI units out there to expect reliable feedback...

I don't know the answer to your question.
The original Onan 5500 in our 96 Southwind works great.
I had one small problem a couple years ago, a new fuel filter solved the problem
I use Sta-bil in the fuel and exercise the generator every month or two.
I think taking care of the generator is the most important thing you can do.
If you don't take proper care of an EFI unit, I'm guessing you'll have problems.
I'm satisfied with a carb, at least for now.
JMO :)