I'd like to argue a bit in favor of the vertical panel. With widescreens being so prevalent and even wider ones on the horizon (ultrawide) it makes little sense to take up the vertical screen space with the taskbar.
On the other hand if you have a browser open, even with 2 windows side by side most pages aren't wide enough to use all the screen space, so a taskbar fits in there as well.
Plus it gives you enough room to make the icons a little bigger and to have 2 smaller icons in the notifications area side-by-side.