I'd say it is a toss up. My only issue with Cummins in my dail(even hourly) visits to Yachtworld, is that it seems that many Cummins powered boats have had one or both engines rebuilt on used boats. And usually with not a lot of time on them. I don't know if they are cheap to rebuild and people do it for preventative reasons.
What I found having replaced more than one Cummins engine in a boat is that there are a high percentage of engines being replaced due to overpropping by the boat builder. There is a strong incentive for builders to overprop, speed sells boats.
Another reason is lack of maintenance, specifically after cooler and heat exchanger maintenance.
Here's a good example, my boat. I have a Bayliner 4788. From the factory it came with 330 HP Cummins 6BTA5.9L diesels. It also came with 24X24 props.
The day the boat weas brand new, with little fuel and no owners junk on board the boat would make its rated WOT of 2800 RPM. Add full fuel, water, a skiff, and all the owners stuff and theres no way the boat would make 2800 RPM.
So, the PO of my boat not realizing he was overpropped drove the boat hard, at high RPMs (Cummins used to recommend running at WOT -200 RPM for a cruise speed). He also did not perform his preventative maintenance on the engine heat exchangers and aftercoolers. Well, a thousand hours later one engine had high blow by and the other was marginal.
When I repowered the boat with new factory reman Cummins engines I reduced the prop pitch from 24" to 22". I can make 2850-2900 RPM with a full loadout, my EGT is running <900 and my boost at a 2400 RPM cruise is around 12 lbs.