Depends of course on the use to which I'm putting the apple. If I had to reduce to a single variety in the orchard, I'd probably grow Liberty (not an heirloom, but rather a university-bred disease resistant variety created in the 1950s). Great eating fresh off the tree (if, like me, you like a tart, but not overly tannic, crisp eater), makes great dried apples, and decent unfermented juice. I would choose Honeycrisp (an even younger variety) over Liberty, if it weren't so damned hard to grow well. For keepers, I'd go with Black Oxford. For pies, it's hard to beat Beacon or Charlamoff (which is known by at least a dozen different names that are all somehow or other derived from Charlemagne, or Carolingian). I also like Calville Blanc for pies.