A low hour Yama OX66 would be a good motor, I hear the 200 HPDI's are a solid motor, Merc I believe has a 175/200 hp Verado. A friend who has a Sweetwater dealership in Sanibel Fla say's the Etec by Bombardier is the heat (maintenance and fuel wise)...

Dont know, I'm partial now because I run the Yamaha HPDI and it's been a good motor.

Take a look at Ed's Marine Superstore, they usually run some decent sales on motor's new and clearance:

http://www.edsmarinesuperstore.com/