In max potential, Berdych. Better rally shot, better mover, more precision, and could be argued he has better variety and volleys.
Pretty much any player has more max potential than Soderling based on such comparison. Luckily for Sod he's got a top serve along with top groundstrokes and is better than most mentally aswell which is probably why he won their last meeting. Not much apart them other than that. You can't use drop shots very often or come to the net either all that much against Soderling because of his power, so variety becomes moot. Berdych didn't do anything but baseline in RG.