I cut my photographic teeth on Canon FD cameras and, once I began to learn a bit about photography, to me, the ultimate Canon camera was the original F-1. Well, this was back in the early 1980s and the original F-1 had been out of production for a few years by that time, but I perservered and found a really beat up copy for cheap at a camera swap meet and bought it. I proceeded to use that camera for the next several years and it never once ever let me down. Despite looking like it had been used as a hockey puck for a few spirited session out on the ice.
Since those days, I've had the opportunity to own and use many cameras of all formats and makes. Some of them were and are brilliant cameras and I'll admit to having a few favorites that I've acquired as a result of these experiences. But when it comes to my favorite 35mm camera of all time, I keep coming back to the original Canon F-1, well actually the F-1n (second version of the original) to be specific. I now own two close-to-pristine examples that I'm almost afraid to take out of the case because I don't want to put any wear on them.
Some runners up include most all of the F-series Nikons: F2, F3, F4, F5, and probably the F6 too. The Pentax LX. The Minolta XD-11 (XD-7 and XD are the same). Contax RTS III. Leica M6.
Medium Format favorites: Pentax 6x7 (all versions). Zeiss Super Ikonta B (late model with the Synchro Compur shutter and coated lens). Bronica ETRSi. Hassy 501C/M. Rolleiflex SL66.
Large Format: too many to mention. If I had to choose one, it would probably be a Deardorff 5x7 field camera.