I've found that verticals give a very even-mellow vape. Full flavor and not too any one thing in particular. I was playing with how the air flows over the coil a while back, and how that affects flavor, TH, etc. On a horizontal coil, I found that the more air that gets under the coil, the more TH and zingy/acidic flavors you're going to get. More air over the top is mellower, sweeter, and less exciting. It seemed to me that a vertical coil is balanced in this respect. There is no top/bottom. I think all this has to do with the fact that heat rises, and that there's more airspace (usually) above a coil than below it (further inviting the vapor/heat to expand in that direction). So, "top-air" is hitting more of the effective area and "bottom-air" is "missing the point". After all that, me being a guy who likes full flavor, but needs some acidity and some appreciable TH, this was my resulting favorite build.
Vertical section for balance (centered in air path), and a very high horizontal coil with almost all the air passing under it, to add the kick.