Tough choice, since I like all of the components in my current system. Sort of like one of the Commandments from "Animal Farm": "All animals are equal, but some animals are more equal than others". I can fairly easily choose my favorite two components, however: my VPI Classic 3 / 12.7 tonearm combo, and my Vandersteen 3A Signature speakers.
Of all your gear, what piece impresses you most?
I like all my gear, yet the single piece that blows me away the most is my phono preamp.