I think the Z-Pipe brand butane insert for the Zippo is superior to the Zippo-branded butane insert, and both are superior to the Zippo liquid fuel insert. Here's my reasoning:
The standard Zippo liquid fuel pipe insert leaves a wisp or more of fuel flavor on your tobacco, no matter how long you "burn it off" before applying to the tobacco. This, plus the fact that the liquid fuel evaporates from a closed lighter far too fast, means that you'll spend more time refilling it than you'll spend using it as a lighter. It does have the advantage of being both right-and-left-hand friendly due to the fire hole going all the way through. This is a nice feature that I wish the others had, and thus it's not a total failure. Grade: C-
The Zippo-brand butane insert has a tiny, tiny spark wheel and a minuscule button that you then have to hold in order to keep the flame going. This, plus the fact that it is all metal such that you have no indication of how much butane is left in the tank, means that it will be hard to light, if there's actually enough fuel left in the tank for your smoking session. Grade: C
The Z-Pipe butane insert solves all of these problems, as it is lit via a larger button that is easy to hold down, and has a plastic fuel tank that you can see how much fuel is inside. It's also slightly cheaper than the Zippo-brand insert (though this cost is offset by you needing to have a Zippo case already). Grade: A-