Hi-
It is wonderful that the new R23 has the option of inboard or outboard!!
We have an R27, and I am a big fan of the economy of a diesel engine. We also have a 20' RIB with a Yamaha 115 4 stroke on it. What a great engine. It is 10 years old now and we have not had a single issue with it. We use it for scuba diving, so it is frequently under a heavy load and running hard. They are quiet and reliable.
I think it is great that Ranger offers that option! Here is my 2 cents on the differences.
Efficiency- The Diesel , you will probably save money over long distances (especially if you are running with efficiency in mind).
Longevity in salt water- The Diesel, unless you wash out the outboard every day or do freshwater cooling. (Presuming you are not trailering it with each use).
Noise- the outboard. Being that far back, it will reduce your noise lever, I presume.
Storage- The outboard. No internal engine = more space.
Jeff