I have both and the Hayes are better for long descents(1 or more miles ) by far but both will stop you under normal circumstances and both have good power and modulation. the Hayes need no adjustments but the Avids adjust very easily. they need that because they frequently need minor tweaking if you dont like noisy brakes.the Hayes are stronger but the Avids are good also. I have 3k miles on my o.e. pads for the Hayes that are still in great condition and got just over 1500 on the Avids before they wore out but the Avids broke in quicker.
flip a coin IMO as they are about the same, price wise, if you need levers and cables.