I know it's an old thread, but I'll just add a few words in praise of the 26" MTB.
I have a GT Avalanche hardtail (2nd hand, cheap) and I've been riding it a lot in this damp spring we're having - and getting well caked in mud in the process. And it is just so much fun. Approaching 60, belting round the woods on the GT is really helping me feel young again!
I bought a second set of wheels, and I have the Tioga knobblies it came with on one set (I have no familiarity with the brand, but they seem great for the mud), and Schwalbe Land Cruisers on the the others for when I'm on firmer surfaces and really don't want the knobbly drag.
I recently saw some Continental Sport Contact II tyres going cheap (£10 each) and got a pair, and I'll put them on my Grisley rigid just for knocking about on cycle paths and the like. (And the £20 I paid for the tyres has brought the total I've spent on that bike so far to £50, including the bike.)
In short, after a near lifetime of riding steel road bikes (for which I still have a passion), I've also come to love the 26" MTB format.
And if you don't need the latest generation of technology for competition or serious technical riding, there's a whole load of 1990's to 2000's generation MTBs going on
eBay for silly money. Every cyclist should try one, at least once