Death Knight - Absolutely.
As to my favorite Death Knight in the lore? Thassarian.
He was the first DK to re-join the alliance, opening the gates allowing the rest of us to do so as well. He was also a really interesting quest given during the acherus line. If you re-do it, you should read his texts.
Gruul: You can solo soak Inferno Strike with AMS + Rune Tap. Oregorger: AMS for Acid Torrent
Blast Furnace: Gorfiends the adds onto the Primal Elementalist's in phase (not the Guards though), massive cleave damage. AMS Soaks Ticking Damage from Heat
Flamebender: Block the Wolves Breath with AMS
Kromog: Breath of Sindragosa during the Breath attack is insanely OP
Beastmaster: Remourseless Winter. 'Nuff Said.
Taking Gorefiends and Defile on Kargath let's you group and then decimate the arena Adds very VERY quickly.
You can use Rune Tap on a LOT of the butchers "Tenderizers" to dramatically reduce tank damage. Dancing Rune Weapons parry can also be used very effectively as "Tenderizer" can be avoided.