The wifey and I have gone around and around with the twin vs single question. The answer is, it depends. Like so many boat decisions, there is not a right answer, just an answer.
The current boat design that has our attention can be had with a single or twins. The pro's and con's have already been discussed and beaten to death.
However, with this design, twin engines with a driveline protected by skegs, allows to the boat to dry out. Being able to dry out the boat is a big deal for us and over shadows the negatives of twins.
Not all twins have a exposed props, prop shafts and rudders.
Surprisingly, I have not seen hybrid mentioned.
I have been very skeptical of hybrids on a cruising boat. A an electric motor is not going to power the boat for days and days at the speed of a diesel engine. In fact, the battery bank is likely only going to be able to power the electric motor at slow speeds for a few hours a day. Having said that, we are interesting in traveling some of the European canals which can have speed limits. Having the engine running for hours at just over idle speed, even on a single engine in a boat with twins, is not attractive. A hybrid on the other hand starts to make sense.
A hybrid as a backup for a single is also workable. It is not going to move the boat for hour after hour after hour at normal speed but it would be enough to get to a place of safety given how many boats are used.
Cost is the big question of course, but if one can use the hybrid's capabilities to replace a generator, the cost vs capabilities equation gets interesting.
Later,
Dan