Don't think the body matters - all Nikon/Canon and some of the 3rd parties (esp Sigma) produce lenses for any given situation and each has their equivalent versions.
When comparing Nikon & Canon lenses in a given price range, in general I think you'll find that the optical differences can only be revealed on the test bench.
At the moment the main thing separating the two is Canon seems to be more innovative - image stablistation is incorporated in a wider range of lenses, and at the long end, Canon have developed the "DO" lens which results in a smaller lens for the same focal length aperture - so far only a 400mm is available, but others are planned.
Sigma is probably the primary 3rd party contender, offering better value for money unless you insist on the absolute best.
In all cases I would absolutely avoid "budget range" lenses - doesn't matter who's name is on them, they suffer in both build and optical quality. At the other extreme, pro range lenses are seriously expensive, and you need to be sure of what you're doing before spending that sort of cash. But in between you're spoilt for choice, and can't go far wrong with any of the makes mentioned. Having a specific purpose in mind (as you describe) should help you narrow the choice - you can always come back here to ask for help in final selection.
But remember, everyone here has bought something which they think is the best choice for their criteria, and all comparisons are relative - when someone tells you a lens is "sharp", this is pretty meaningless unless they can tell you its "sharper than X".
For what its worth, my current "best choice" outfit consists of a Sigma 14mm, Canon 24-85, Canon L 70-200 f2.8 IS
, Canon L 300 f4 IS
and Canon 2x and 1.4x convertors. All these lenses are in constant use, and I would be hard pushed to part with any of them. I also have a 50mm but don't use it.
I would consider my outfit complete and capable of pretty much any task I put it to, but, if I won the lottery, I would add a dedicated macro lens and the Canon 500mm f4 LIS
Colin K. Work, Pixstel