Re: Which engines would you think twice about
IMHO, if you've got a choice, get a Yanmar. I've had them on 2 boats and never did anything to them but oil/coolant changes and impellers. They were rock solid for us YMMV.
We've had a couple of fresh water cooled Westerbekes and a raw water cooled Volvo. Made them both work (I would not take them out of a boat, or eliminate a boat from consideration that had one), but they were both more trouble. Seems like we were always fixing some little thing, but with attention they were reasonably reliable. Volvo was definitely the hardest to keep running, but it was raw water cooled, and 20 years old, so who can complain?