The mountains are beautiful, but I'd take the tropical island. It would be warmer and would have higher biodiversity, which would make it interesting as well.
Usually power. I tend to naturally have a faster than average cadence, and I like the exercise aspect of it. If you're not sweating and getting your heart rate up, it ain't exercise. In fact, I just may go for a nice 10 mile walk today, now that it's stopped raining (been raining here the last two days).