What type of twin-tip ski should I get?

I would look at K2, they make incredible all mountain skis, and their 9-10 line is especially impressive. They have some park specific models, and some that are slightly fatter. I ride the extremes, and they are very fast on groomers, and flexible enough for some/most park (not so good in the pipe) However, they can also handle pow days. If you know how to ski 'em, they can handle thigh deep days, but are perfect for about 15-20 fresh inches and the ever so often eastern hard pack. I also recommend armada, they are a growing company that knows their stuff. Lastly I would look into line skis and possibly surface.

I have the Line chronics and i push those hard on just the mt. and they hold up just fine. I won a four cross and all the other races my freestyle team does on them. They will hold in almost anything, ice, crude, groomers, fresh pack, just about anything. I haven't used them in any real powder because i live in the midwest. and there is no powder. but for the little bit of powder i skied in CO when i was there they work pretty good. They will also throw down in the park. I still have yet to find a weakness other that you can't center mount. but if you plan to spend most time doing all Mt. then that won't affect you.