Since this is a 35mm camera area, I'll stick to that format. In 35mm it's Nikon, unquestionably. I've had at least one, and as many as four, of their SLRs in my possession for most of the last 20 years and I have shot many hundreds of rolls of film with them. At the moment I am down to just one F3HP.
I've also got Pentax, Olympus, and Canon cameras floating around but they don't see a tenth as much use (the Pentax is a "collectible," the Olympus cameras are point-n-shoots, and the Canons are really my wife's cameras).