I vote for the '97-'98 Deore XT M-738/739 rear derailleur:
Four different cage lengths (although the SS is a rare beast), works with everything from friction to 8 speed, and damned near indestructible.
Anytime I come across these I try to snatch them up.
A close second would be the '97 STX-RC R. DR... same body profile as the XT, but with a steel cage.
Hope everyone here in the States voted today... exercise your right!
