My favorite type of bicycle would be a road touring bike, possibly an older road racing bike, with ample clearance for 32 or even 35mm tires, and with medium-range gearing, something on order of 40 to 95 gear-inches.
Having said that, my mountain bike has been getting a lot of use lately, mostly on road, some on multitrack trails. (I don't do technical mountain biking -- don't have the coordination for it.)
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069