Which Audio Research gears are classics?

Which ones to hunt down on used market?
You want to hunt them down for the sake of owning them or because of their musicality? The D79, D150, SP3 are all popular favorites of the products in the 70s. But for many of us ARC fans, it was the SP-8, SP-10, D70/115/250 and M100 models that were so special. Ten years later the LS5, VT130 and VT150 brought another opportunity to enjoy that wonderful ARC musicality. I have not heard that magic since in any other ARC products but I must confess, I have not heard the high priced REF products.
The spider gear and the planet gears are the ones to look for... A lot of folks head straight for the sun gear, but most of them wind up getting burned.

Did you know the word "gear" is actually plural when it refers to a group of like components (eg., "camping gear," or even "audio gear")? Perhaps you were speaking metaphorically, likening a preamplifier to pinion gear, for example.

I see this common mistake all the time and it drives me crazy. Thank you for the opportunity to vent. :)

The original SP-6 preamp and the SP-14 preamp are good ones to look for too.
I have listened to the SP6 and SP8 pre amps and prefer both in their original models, the B versions are bright. Also the SP11 is very highly regarded. And of course the D79 and D150 are probably the most famous and musical of all their amps.
The D79 si by far the most desirable.I use to own a solid state monster the ARC D110B which was great on bass, The SP-6B and the Preamp SP-8.
I wish I would have kept those preamp's still today.The SP-6
could warm u up nicely on a cold winter night.But I think
I would take a D79 Amp and mate it with a SP-11 Preamp and then I would be very happy on my stranded Island provided I had electricity. Happy Hunting!
The above responses are right on, I have never owned an Audio Research product I didn't like but had some that really stood out in terms of sound quality. I think the ARC LS-1 represents an excellent value for its used price but is often overlooked because there are no Audiogon reviews or posts on it. I have compared the LS-1 to the LS2 & found the LS-1 to be more transparent, with very good dynamics.
I like the D-75A, got one from a friend and restored it with 99.99% original parts. Its 70WPC and all tube, baby! Generates a lot of heat but it has been reliable; weighs a ton. Have not heard much about this amp here, but its very very nice, great sounding.