I am originally from Steuben county and I gotta say I desperately miss the twin tiers.
There's nothing like the Alleghenies, and upstate NY harbors some of the most unique portions of.
Even areas in counties around the southern tier have beautiful visuals. Look around southern Ontario county as well, gorgeous area with high hills.
The Olean area is one of my favorites. A perfect cousin to the Catskills at the eastern end of the southern tier.
And I just want to add that even though the sub-region "Appalachia" terminates in southern NY, the Appalachian mountains and foothills themselves continue on all the way through New England and Atlantic Canada.