Personally, I think a 1000 beats a PC-12 every which way. Faster, burns the same or less fuel, two engine redundancy, costs the same or less to operate. Yes, slightly less room and not as nice a lav. So if you need to carry 8 people around all the time, the PC-12 is going to be better. Or if you need that giant cargo door and carry lots and lots of stuff. But for most usage, 1000 all day, every day.
Merlin IIIC is an even better choice if you need to carry 8 people all the time. I used to fly a Merlin IIIB and our normal passenger load was 7-9 (with two pilots). The passengers loved it-- quiet, outstanding environmental system (so plenty of cool air), fast, just great. But nowhere near as nice to fly as the Commander, and doesn't perform nearly as well.
The single engine PT6 thing is because Pratt will sell the OEMs the engines very cheaply, but because the engines are so expensive to operate, you can only justify having one. Fortunately, they never fail (except for the PC-12 last week, and many others...).