Cummins would be my first choice ,cats and older Detroit's are OK IMO . no fan of Volvo or Mann and MTU do to cost of repair and service. you did not say what age your looking at so you choices maybe limited , different makes may offer different option's on engines , limiting you choices
I like ZF gears myself , But most others are good and if buying a used boat or even new you may not have a choice .I don't know of any that would be used in this size range boat I would run from .
what boats and age brackets are you looking at ? Are you even thinking of a glass boat ??