I have had experience of both these engines in Vega 27 boats. I have found teh Beta far superior. Based on a Kubota so a very popular engine. Fresh water cooling is much preferred as you do not want salt water going round the engine. The fanbelt problem on the Beta was caused overhot engine rooms in a few boats. This has now been cured with a higher temperature rated fanbelt. The water pump on the Beta is driven by a gear and not by belts. I think the Lombardini also has a cambelt instead of chain, again not ideal in a marine enviroment. Hope this has been of some use. If I can help then email me on steve@albinvega.com