To provide a recommendation depends mostly on your requirements - vessel hull design, design speed, duty rating and propulsion system. I've powered a lot of aluminium boats I've built with various CAT engines for both jet and shaft drive - patrol craft, hs ferries and pilot craft because the CAT engine duty ratings provided best and cost effective options but for big boats - 30m to 60m I personally prefer MTU for long range performance, technology and their warranty. When spending $2m plus on ME's it's reassuring to know that if there are engine issues the manufacturer while go 100% to solve the issue even paying for a hull rebuild if you have to replace engines thru the hull or lift the deck for access.