>>1655122New bikes come with benefits like a warranty, normally new stuff has a longer life, but with bikes it's a bit different. Late 80's to mid 90's was when mountain biking was the period when mountain bikes went from niche specialist bikes to mainstream, there wqas a lot of innovation and the overall quality of mid-top tier components was far superior than their equivalentsa today.
I emphasized good condition and that is key, look for a bike that has been well looked after, preferably one never ridden in anger, you'll pay more but you'll be getting a bike that should serve you much better than a similarly priced brand new one, plus it'll have soul.
You want to look for chromo steel tubing,terms like Reynolds 501, tange etc usually signify superior quality.
Seek out LX, DX, XT or XTR componentry, check for damage to the frame, take it for a spin, if everything feels good and you like the fit you have a bike for life that will only increase in value if you look after it.