I have had both but currently have twins and triples. Never really measured but figure the twins to be less fuel efficient. Your real question is which will you be more happy with. Spend the money on twins. Two mild engines should be less temperamental than one boosted motor. It will handle rough water alot better and be more maneuverable around the docks. When you break a shaft, prop, gimbal, etc. you can still limp home without a tow. You will pay more know but your resale will reflect this also.