Have the KG back, and like it a lot. Its rugged, simple and gives a lot of options (the three way version) easily. The Maxwell screen is just lovely - I use a Hoodman sometimes, but often nothing is needed. The screen is that bright. Alignment seems right on as well. Its a bit thick, so a 35XL won't work, although a friend has a 32 which works fine.
The Linhof back has tighter tolerances, but is less flexible. The longer one is huge and heavy, and can act like a sail in the wind.
The KG can change mounting plates (camera and back both) and is pretty easy to work with. I had to send mine back to KG for some repair work, especially on its teflon sliding strips, but Keith (he's KG) is most friendly, fixes it without questions and reships in about a day. Might be a hassle overseas. The other issue is tolerances in the back - it seems that there is a wee bit more room on the back as it slides than on the Linhof or Silvestri, but in shooting and looking in detail at images, it doesn't make a difference. THe KG is rugged and well made.
The Silvestri back (not sure about the Linhof) has firm locks on the sliding, which the KG doesn't. If you plan on carrying your camera around with the back on it, think about this somewhat. That's the biggest issue I have with the KG back. The latching is spring loaded, not locked. Other than this, its a good solution.
