Are you one for riding around all day, do you intend on pulling skiers, tubes, etc. will you be using it on a lake in the harbor, ocean, etc?
Here's my opinion:
For me, small boats are just easier to deal with, after years of hauling monsters around the marina I'm not interested in dealing with behemoths. Small boats are also easier to pull down the road, might take mine out west with me if I ever go again.
So yeah I like my small single engine Sportster 951 boat for the kind of boating we do now short distance day trips where we (2 of us + small dog) stay in one place for most of the day but it's a weakling when it comes to pulling me out of the water on a slalom ski. I'm a firm believer in making the boat do the work and with this thing I have to work too hard, except I don't ski much anymore, maybe that's why? Well, I could always splash my old-school big block jet boat, it;s got a killer hole shot.
Anyway, if we were doing a lot of riding around and skiing all day, I'd rather have a stern drive for fuel economy and especially the pull your arms off grunt. The 4.3 V6 is quite the runner in something 19ft or so, the 140 4cyl does fairly well if propped right (I've pulled 4 skiers using a small wheel) but isn't a speed boat engine.
The 2-stroke Rotax engines are the least expensive motor on the water but they do wear out much faster than a big hunk of iron does so then again if you put a lot of hours on then the Rotax might not be for you.
Another thing to consider is how fast you want to go, some folks can't get enough speed but for me a 30 MPH cruise is plenty. If your water is rough like in a bay or crowded lake, a larger boat can help. Narrow and long will cut through chop where short boats will experience a bone jarring ride. I just go slower, my dog doesn't like bouncing around.