Honestly, it depends on your intended use. I got a steal on a bluebird Ar3 with a 5.9
I don't intend to live in it or full time. I can take the smaller engine.
If you plan on traveling and encountering mountains, you may want to 8.3
I don't like CAT motors. It is based on what parts and service cost, not dependability.
A dt466 or 8.3 mechanical would be my choice if I were planning on full time traveling.
The coach work I have found are very similar in the 3 you mention... Thats like asking if you prefer Ford, Dodge, or Chevy.
Flat front fe busses give you the most floor room, but limit your under bus options, RE lose a bit of space, but you can use more under bus area.
Big, medium, short depend on you.
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