Darius is easily countered by Kayle. If Kayle goes AD or AP make sure you used move quints and ensure that you take your Q by level 2.
AD: Rush Zeal then Boots
AP: Rush Aether Wisp then Boots
Simply Q him, back right away to dodge his pull, then auto atk with your E active. If you do get pulled self cast heal (W) and speed away to re-Q and continue fighting him.
Hope that helps,