What's the best bicycle rear derailleur of all time and why?

For my money, on a mountain bike, it’s been the Shimano Deore LX. (It’s gotten some alright reviews, too.) Twelve years and still going strong on my full-suspension, even when practically everything else has needed replacement.

For my tri bike, I’ve got Shimano’s Dura-Ace 7800. Still, only about a year on that, but so far it’s been rock solid, seamless shifting.

As far as the best available at any price for a road bike, I’ve always heard it was Campagnalo. But I’d also like to hear anyone’s personal experience.

I have two road bikes: one 3-year old alum frame with ultegra and an old chrmoly from the late 80s with Campy Athena. On the ultegra I have already replaced the chain, cassette, and I’m burning through the big ring. Dérailleur is hanging in there for now but its wearing. The Bike with Campy I have crashed, sweated on, cleaned rarely, abused horribly and never changed a thing. Its on my trainer still and I ride it in winter.

Campy anything.

. The The on, crashed, cleaned rarely

I’m still waiting to hear what people have to say about SRAM Red

But so far I am a huge fan of Dura-Ace (I have an 8-speed D-A rear derailleur that is 13+ years old and still has no problems whatsoever).

On my MTB I have Shimano Deor XT, and its a very high quality dérailleur, the next one up is XTR. So you can’t go wrong with either.

I do have the first edition of SRAM’s derailleur, but I never installed it on my bike.