24-120mm F4 VR or Canon 24-105 F4L

I've owned the Canon 24-105L with the 30 and 40D and it was my favorite all-time walkaround. I also owned (in Canon) the 24-70/2.8 and just about every other L lens below 400mm primes. I moved to Nikon in 2008 over the issue that Canon DX bodies just weren't keeping up with Nikon. The D300 was a great upgrade to my 40D. That said, till the 24-120/4 came out, there simply wasn't a piece of AF-S Nikon glass that matched the focal length and IS/VR of the 24-105L. This new lens does that!

I've not used a Canon body since the 50D, so I can't comment about what you would get there, but a D600 and the 24-120/4 is just simply sweet. Built like a tank and focuses lightning quick.

Now that Nikon is matching Canon on the lens lineup, I truly believe Nikon is the path forward. A 16-35 or 12-24 (no VR sadly) plus the 24-120 and now the 70-200/4VR make a powerful lineup. Mated to either the D7k for DX or the D6/800 and you have a combo that's reasonably priced and will hammer anything from Canon.

Used to be all you saw at sporting matches were the giant white L's. Now you see a good mix of the white's of Canon and the long black lenses from Nikon. There's a reason for that.