this is an arguement that will never die, never. best is to try both and then cook the way that floats yer boat. me? i use the lower vents to control the temp and the top to micro manage if needed but the top is never closed more than 1/3rd. i first used the top vent but found i had a hard time controling the temp. if that was so, why all the vents ? to me and i was the first to mention it is to cover the lower coal grate with foil so you don't mix hot and cold air together. to me that is a big differance in controlling the temp.
spam, can't live without it