Amarillo. I don't use it as much as I should but looking back at all of my best home brews amarillo is the common factor.
I use Magnum for bittering almost exclusively. I always have Cascade on hand to knock out a nice pale ale, and some selection of Citra, Galaxy, Mosaic for something fruity.
I do also love Lemon Drop in a pale or wheat, but I find it tends to fade fast so I use it only in things I intend to drink quick.