We found that the upright cooker was easier and more predictable because the insulation takes weather variables out of the equation. I think we got a better smoke flavor with the horizontal cooker but that is mainly because you have to burn sticks rather than charcoal. I honestly don't think we used enough wood in the upright cooker, there is a whole lot of space in that thing so it takes a lot of wood to fill it up with smoke. For what its worth, I am going to start building one similar to the upright cooker for myself in a few months. I love my green egg and have fun cooking different stuff on it, but once you cook on a Backwoods style smoker, you may never go back.
This is a friend who is building a "knock off" of the backwoods smokers (original vertical reverse flow insuated smoker).
https://www.facebook.com/Woods-Custom-Cookers-1458649091116747/?fref=ts
His "knock offs" are winning every pro competition in our area, if I had the money I would have one, but i dont so I am going to build one worthy to be called a "knock off".