>>1719572The best thing to look out for is a few simple names. For frames you want steel, look out for Tange, Prestige, Reynolds, Ritchey tubing.
Groupsets wise you want Deore DX, XT or XTR, or Suntour XC-LTD, XC-Comp or XC-Pro.
Avoid V-brakes, there are some excellent bikes with V-brakes however there are many many more bad ones with V-brakes, they arrived on the scene in the mid 90's at the time the multinationals began to finally take control of the industry and they herald the beginning of the end for the golden era, so they serve as something of a marker. The same with 27 and 29 inch wheels, there are some great bikes with those sized wheels, but if you're looking fro a classic mtb from the halcyon age then it has to be 26''.
Also avoid suspension, 30 year old elastomers suck, finding replacements can be an awful drag and expensive, plus servicing and maintaining the forks is a ball ache, they weigh too much and just sap energy.
TL;DR
26'' quality rigid steel frame with mid to high end groupset from 1985-1996.
