I haven't re powered but I had a friend who has (2x I think) and the last one was a 55hp Volvo. The OEM engine
was Volvo and I don't know the second. They are very happy with the Volvo. I've helped deliver the boat and it's very quiet and reliable (but it was pretty new too).
Some considerations are what's involved with new mounts, prop rotation and configuration and so forth. Volvo parts
seem to be very pricey. I have one which is 23 yrs old and runs beautifully.
Yanmars seem to be very popular, but look at some of the exhaust
Why don't you get quotes from several mechanics and hopefully ones who know both engines???