Here is my VERY BIASED opinion:
With marine power, much like a car, it is rareley the ENGINE that gives you trouble, it is all the crap bolted on to it. With your outboard, the innards are DRY and ABOVE THE WATERLINE. With your sterndrive, you have the following in the watter all the time:
Cast Aluminium (Does not repel corrosion like extruded plate)
Cast Iron Manifolds (Does an impression of an eroding urinal cake)
Outboards typically go a long time, and then explode gracefully. With inboards, they will nickle and dime you to death, with a constant influx of starters, solanoids, plug wires, carbourator kits, etc. And don't forget that big (usually black) repair bill hanging in salt water all the time, you had better be sure you REALLY have the bellows, gaskets and drain plug o-rings on, because it is underwater, usually 2 or 3 feet down where there is a lot more then just atmospheric pressure pushing on the weak links.
Quotes from some my sterndrive days:
Gee, my Mercruiser manifold with an 1/8th inch gasget surface between the riser and manifold started leaking right at the back where I can't see it, all over my starter and shift-interrupt (Means that the engine will not start untill you wiggle it to the neutral position)! (And don't forget the exhaust valves, but don't worry, you'll know about them soon enough).
Oops, my oil pan rotted through because it was 3 inches above the bilge.
DANG, barnacle grew near my bellows, tilted the leg up, and RIPPPPPP.
Let us not forget that you are not supposed to bolt "car" starters, altenators and carbs on, you need special "marine" ones with flame arrestors, spark guards, and other "fee for option" add-ons.
With an outboaard, 50% of the electrical system is up under the flywheel, nice and dry, and it is also solid-state. No more alternator wires rotting off, or bearing packs seizing, breaking belts, and leaving you to putt home on, you guessed it, you're trusty OUTBOARD kicker (Try pullin your anchor with your kicker, it's FUN).. You have a much higer hill to climb with your fuel, lessening the chance that water will make it's way up it (You should have a good clear-bottom strainer anyway).
Don't forget, when you poke a hole in your hull, your outhoard will be high and dry, as I found when my Campion Fishing machine busted open at Swiftsure. If I had a sterndrive, it would have been under 18" of water, and may not have ran enough to plane the boat to keep me above water, and you may not have my long-winded rants to put up with today.
So yes, an inboard with an automotive engine may be more familiar to us handypersons, but with a good manual, an outboard is a breeze to service, does not spend it's life in salt water, and provided it is not a decroded old piece of sh**t that hasn't gracefully blown up on you, is easier to keep ahead of things on.
