There are a bunch of awesome boutique vintage mountain bikes (Salsa, Fat Chance, Steelman, etc..). However, I don't have a bunch of money to spend, so my taste leans toward the bigger brands. A 1991 Diamondback Axis Team is my favourite, but I may be bias due to the color.
I'd like to find one in my size one day, but the chances are slim.
When it comes to vintage mountain bikes, they work best as all around, commuters, fire road and gravel bikes. Riding technical singletrack is what the new bikes are best for. I know a few that can fit 26x2.5 tires, such as the Trek 9xx series, but max tire size depends on the bike.