Listen to these people. The Faction Candide 2.0 and 3.0 are good, the 2.0 will be more park oriented and the 3.0 more big mountain oriented. The ON3P Kartel 106 would also be a good option, probably the best one. On the heavy side, but it’s bombproof.
To be completely honest, skiing rails and big mountain is definitely possible on one ski, but I’d suggest getting dedicated skis, even if it means you have to wait a little bit. Big mountain skis won’t lend themselves to rail skiing simply because they aren’t designed that way. If you had to get one ski, look at the Kartel, the Moment Deathwish, or either of the Candides.