Schwinn Continental (unknown number of times; no odometer in those days)
Schwinn Le Tour (once)
'80s Fuji 12-speed (once)
Trek 560 (probably 4)
Specialized Hardrock (once)
RANS V-Rex (about 12)
The Le Tour was horrible. The Fuji was pretty uncomfortable. The Trek was okay when I had a good back. The Specialized was actually the second most comfortable bike I've finished a century on. On the RANS I did six centuries back-to-back, quite comfortably.