What’s the most underrated used Audio Research gear?

SP 14, advertised as better than the sp-9, based on sp-15 technology.

Dual 76B and SP3-A-1. Much magic there. Especially when used to drive Maggie Tympani IIIs. 

17 is a great pre… the HD amplifier is a brute of a sleeper… hybrib tube / SS

One you will seldom encounter or hear about are the mono tube amps: VM220.  Magical.

I've been using an ARC LS7 that I bought used back in 1998(!) and it has consistently been an absolute champ. I have turned it off a handful of times in that period, and never changed a tube. what a demon!