Hi Donald and Diane and
! I don't think I greeted you since you have been hanging around. You have a good question and I think you can get some biased and non-biased opinions around here and you will have to be the one to sort through the rubble. You will find some folks that may love one engine over the other while being in disagreement with another person having had or enjoyed a great experience with the same engine, while another person may have gotten screwed over on a bad engine in a coach when they originally purchased it. To be honest all those engines are great depending on what you are after.
Your 8V92 as long as it is a Silver Series is a pretty descent engine. Silvers don't have the leak problems and have the better component options. From talking with several mechanics over the years the DDEC 4 is the best choice of this engine. Engines with computers normally last a lot longer then those without. Just better engine management. Parts are not all that bad to come by for this engine, the biggest problem is there are fewer mechanics that know the engine then there was 10 years ago and in the future that number will surely continue to diminish.
Series 60 Engine is my first choice in a coach engine and this is the most commonly found engine in the bus fleets, in fact thousands of older still on the road Greyhounds and other tour buses have been converted from the two-stroke engines to the Series 60's. A lot of that could be due to emissions and fuel savings. A half mile to a mile per gallon in a fleet means huge savings. This engine is a great choice and tons of parts and guys that know how to work on them. Two less cylinders to worry about.
Cummins has made several great engines and have an easier time meeting emissions standards than probably any other. Parts and service are not all that bad either. Depending on what coach you are considering, you won't find many Cummins in the high end luxury coaches unless it's a very late model Newell or the last of the Wanderlodges. Of course there are a lot of common chassis built motohomes that come with them.
There are a couple of other engines choices out there you didn't mention like CAT, International, Volvo and Mercedes. CAT's are the most expensive in my book for parts and repairs, besides they have abandoned the RV or highway industry and are currently sticking to off-road only. For the time being anyway, with them mainly having an issue do to not wanting to deal with the emission standards. They are reconsidering the market again. Newell Coach Factory engineers have been talking to them as are other RV chassis manufactures. Volvo is that standard in the Newer Prevost Car motorcoaches, the main reason being that Volvo now owns Prevost.
We do have a few other straight shooters hanging around here that will surely chime in and share their opinions.
__________________