Best way to carry a D4

Another vote for Black Rapid. Best strap I ever had.

As mentioned there are a lot of different models. I recommend going to their website and look for the instructional videos so you can see how they work.

Just a note: some folks (including Nikon IIRC) caution against hanging the camera upside down by the tripod threads. Me, I used the black rapid with a F100, an F5 (similar to a D3/D4, probably even heavier), and a D200 and never had a problem with any of them.