For a traditional group like you've mentioned, DK tank (and driver/master) is quite easy. Most tools for managing aggro it seems. I have switched to shamans for heals (they are OS with Ele for scenarios etc) and then Hunters and whatever. Both my main teams are now 2 hunters and either a elemental shaman or 2 hunters and a mage. I occasionaly drag a Subtle rogue around (found a really good 1 button macro for single and aoe on lazymacros.com) but a few extra mechanics to handle the melee dps in the group.