Race bike: Fred Williamns Lightweight Special was most exciting road bike, not light compared to today's carbon superbikes but railed round corners and was comfy for a race bike of its day. And had a certain character to it too. Recently reborn as a fixie.
Tourer: Dawes. Comfortable, reliable, load lugger. didn't pretend to be anything else, just got on with the job.
MTB: Zaskar, for a super light XC (22lbs) bike it was very comortable yet climbed like a rat up a wossit. Tought with it.
Folder: old Birdy Blue. Seemed a lot faster than the modern Birdies.
Tandem: Burley Samba. Tough, comfortable and, for a steel tandem, light.
Of the above I think that the Fred has the most miles on it by a long chalk. Pity it's getting too painful to ride, and the odd spot of rust is showing through. Would have it poweder coated by the fork and rear tringle are chrome.