Canon 5D Mark II
The 5D Mark II has such high resolution that you’ll need extraordinary lenses to make the best use of all its pixels. Canon’s pro fixed f/2.8 super teles are great, but the state-of-the-art in Canon wide zooms isn’t there yet.
Mediocre lenses will work at least as well on the 5D Mark II as the 5D or older cameras, however the 5D Mark II’s high resolution will make any lens limitations more visible. To get the most out of a high-resolution camera, you need the best lenses you can get.