My picks...
Overall, currently... the Dura Ace 7803 rear derailleur and the Mountech front derailleur. The 7803 is the last beautiful polished DA RD. I'm using it 10 speed, with a 12-32 cassette and a 28/38/50 front crankset and a 11-30 cassette and 34/46 front.
The Mountech- as mentioned before- it handles anything, it has a huge range, it's rugged AND it's lighter than most racing FDs.
IMG_1715 by
Dave The Golden Boy, on Flickr
MountechFD by
Dave The Golden Boy, on Flickr
Then if you're going to go all full-on CnV... Again Mountech FD. As
nlerner brought up- the XC 3 pulley derailleur was probably the best shifting friction derailleur I've had. But it's heavy. Then there's XC Pro/XC Comp. Those things feel so great- and they look super.
Suntour XC by
Dave The Golden Boy, on Flickr
Suntour XC Pro Medium and Long Cage by
Dave The Golden Boy, on Flickr
One model I don't recall seeing here- the all-time champion- the Suntour V-GT Luxe. Tougher than pretty much anything, as light as it needed to be, dirt cheap and was in production for like a decade.
Suntour V-GT Luxe by
Dave The Golden Boy, on Flickr