If you're only getting 1 pair, I'd say between 95-105 mm at the waist, twin tipped, and medium flex. BUT: 105 might be a bit much to handle on shitty days or in the park, though some would beg to differ with me on park skiing on 105mm+ waisted skis.
Ideally, I'd say 2 pairs: One at around 85mm (think AR6), one at 105mm-ish. Obviously full twin on the narrower ski, with your powder skiing preferences (big lines vs booters vs all over the place, etc etc etc) determining the tail on your wider skis.
Some people love softer skis at Whistler, some people love really stiff ones. Personally, I like a little softer, nothing too stiff. But, if you're charging hard in a coastal snowpack, stiffer is sometimes nicer, so ya....
There's a lot of variables when it comes to picking skis. In the end, you're the one riding them, and no matter what a bunch of idiots tell you on the internet, if you don't feel good about what you're riding, you won't ride well. So go with your gut on this one.