Good 90's mtb's (by good we mean well designed well built bikes with high quality steel frames and top tier componentry) are the peak every-man bike, light, durable but also comfortable, the geometry means they are perfect for multiple roles, especially for what most people call urban cycling, ie riding around on dreadful roads and transitioning to and from pavements, on gravel or dirt roads etc.
But it is their flexibility that really sets them apart, want to go faster? do a 700C skinny wheel conversion or even keep the 26'' and slap on some slicks, a set of drop bars and you have a comfortable, quick and nimble road bike, put the knobblies back on and you have a gravel bike, put the flat bars back on and the slicks again and you have a great commuter.
Another great thing about '90's mtb is the industry hadn't yet quite managed to achieve 'built in obsolescence' nirvana, a lot of those old components are better than their modern equivalents in terms of the workmanship, the quality of the engineering and materials used, assuming you can find good examples.
for £200 and a bit of luck you can pick up a bike that would cost you £1500 today, sure it might require a bit of effort to restore it to its former glory, but if you do the work you'll have something fairly unique, they are also unstealable in the sense that a good 90's mtb looks rather like a shitty halfords/walmart tier sub £100 modern bike, although the similarity is purely superficial and only connoisseurs are going to be able to recognize the true quality.
They are the best bikes in terms of bang for buck on the planet