I find myself staring at my hotkeys a lot when I play DRK. The mana thing isn't such a big deal when you're tanking gritless, so it's not as big a thing. It's the procs and oGCDs that distract you. You can clump some of them in groups to lessen the degree you need to keep track of them, but it definitely makes DRK the most prone to distraction.

WAR is very straight forward with very few oGCDs to worry about, only have to really keep track of berserk use, cause with it, that's when you start popping a bit more oGCDs and get active in your rotation.