Of the remaining ones I'd prefer the Nikons. They are more functional and have a physical design that (for me at least) makes them easier to use. If you're tight on money go for the D50, if you can afford it I'd not go for the D70 but rather for the D80 that replaces it. If you're looking at the used market for a D70 then at least get a D70s, it's more functional.
The low end Canon cameras are limited in functionality at least more so than the Nikons.
As you go up the scale however both brands will give you good pictures. Even so, I'd still prefer to stay with the Nikon. Nikon has a history of producing fine photogrphic lenses and other accessories that meet the needs of professionals. Canon has a similar history but they're not usually as comprehensive as Nikon. Nikon is something you can grow with in the longer term.
The other diffrence is that Canon like to be wiz bang. They will often build in features that sound appealing but are things you'll never use or care about. Nikon is more conservative, they build in what you need and will use and they don't load their promotions with a lot of hype that has no value.
The cheap part of an SLR is buying the initial camera. Later as you get more sophisticated you'll add lenses and a flash at minumum. Now you're into a situation where you get locked in.
That's the real issue. So think about what you'll do picture wise for the next thirty years or so and look at which camera maker will give you the gadgets you need to make that happen. Then buy in and get the most out of it.
When you compare makers don't get hung up on a feature that one has that the other doesn't. Whatever one doesn't have they eventually find a way to provide it too. The real question is whether a specific brand will meet all your long term needs, nothing more. That's why I tend to prefer Nikon, they tend to consistently deliver high quality solutions for whatever the professional photographers need.