It depends on your intended use(s)
I own the Canon 5D. I went with Canon because I love their lens selection. Especially their Pro series "L" glass. These are some fantastic lenses.
I use the 28-300mm "L" series zoom lens almost exclusively when I travel. With this lens you are prepared for almost any situation and you really cut down on lens swaps which helps a lot to keep dust out of the camera. I just love this lens.
I also wanted a full frame D-SLR and at the time, Canon 5D was the only option without going to their flagship 1D line. Nikon did not have a full frame camera at that time, at least in my price range.
What does full frame do for you? Well, I'm glad you asked
You do not have to apply a conversion factor to your lens. For example, my 28-300 zoom is exactly that. If you have a 1.3 sensor you need to multiply the lens by that number making your 28-300mm zoom into a 36-390mm zoom. Although this helps with the telephoto aspects of the lens, it really messes with the wide angle lenses. It gets worse if you get a 1.6 sensor.
I hope this helps you out. I also take pictures semi-professionally so the investment I made in this camera/lens combination made sense to me. It probably won't for you.
Just think about what you want to do with the camera and decide if you can live without a full frame sensor then either camera will be good for you.
Take care and good luck.
Rick