The Nikon is better because you can put a Leica R lens on it w/ a lens mount adapter. With the Canon, you have to put the Nikon mount on the Leica lens, then use the Canon FD to Nikon adapter in back of that. A little too fiddeley for my tastes. On the other hand, you can spend $40 for two adapters and use Nikon AND M42 lenses on your Canon, so there's that. Gives you an amazing selection of great glass to shoot.
I prefer shooting the Nikons for a lot of reasons, but both are fine, classic SLRs.