Mine is at the bottom and hidden until mouse over so there.
My problem with Taskbar at the Bottom is that the mouse pointer has to be aligned with the Taskbar to make a selection. If you are not careful the pointer disappears off the bottom of the screen. That doesn't happen if the Taskbar is at the top. So to make a selection you just jam the mouse to the top of the screen and slide left or right.
This saves me 250 milliseconds per selection. It adds up. ;)