I will try to be as impartial as possible here. Both Canon and Nikon make some simply stunning lenses. As already noted, it's worth checking that if you have any specific requirements that the manufacturer does indeed make that lens.
Although it doesn't make any difference to the photos note that the Canon's and Nikons attach to the body in different ways - the Canon twists counterclockwise to lock into place, whilst the Nikon twists clockwise. Also, any zoom rings on Nikon are the reverse of Canon, so on a Canon lens, a 24-70mm would read on the zoom ring as you look at it, as 24 on the left, twisting round to 70, whereas on a Nikon lens, the 70 would be on the left, and as you twist it goes down to 24. (I'm not sure I've explained that entirely well??).
The other thing to note with Nikon lenses, is that depending on the body, it may not have the ability to autofocus. If the camera body you purchase does not have an in-built focus motor, then if it's not an AF-S or AF-I lens, it will not autofocus. With Canon, unless otherwise stated, all EF lenses have the motor built into them and so will autofocus regardless of the body they are mounted on (the EF MP-E 65mm f/2.8 is an example of a lens that won't autofocus - but it is a very specialised lens). That said, you did note that your Nikon body of choice would be the D7000, and this does indeed have a focus motor so this won't affect you. But it's just something you should bear in mind as a difference of the lens if you should ever wish, say, to put a lens on a D40 or something that doesn't have the focus motor.
Another thing is the aperture control. In Nikon, this is mechanical. There is actually a little catch on the back of the lens, which you can manipulate with your finger and see the aperture open and close. Canon's are all electronic, so you can't do this. On the subject of aperture, Nikon also make their D series of lenses which have the aperture control ring on the lens, so if you wish you can manually stop your lens down to whatever you wish. No Canon EF lens (that I know of) allows you to do this.
Optical quality between Canon and Nikon is subjective. Both companies make fantastic quality lenses with the Nikon 85mm f1.4G, or Canon 85mm f/1.2L, etc. But equally both companies also make comparitively cheap lenses such as the 18-55 kit lens and slow 70-300's etc. It really is 6 of one and half a dozen of each other. The camera you attach the lens to will have a lot to do with how the lens performs too. But I hear great things about the D7000. Not so sure about the 60D as I've not had any experience of it but I'm sure it's a fine camera. I believe it has the same sensor as the 7D so should be more than capable!
Regarding third-party lenses, most manufacturers make their lenses for both Nikon F mount and Canon EF mount. Zeiss and Samyang lenses are all manual focus only. Sigma, Tamron, Tokina etc should be AF.
Hope that helps.