Every comp can do gold. If you have no idea how to play dk then go with warrior. Even though warrior is probably the worst tank for cm's it will still be better than a dk that is played badly.
When it comes to holy paladin vs resto shaman they both work. Holy paladins bring more defensive cooldowns with sac, hop and wings while shamans bring an aoe stun.
To complete cm's you want to look up what pulls to make, you want to pre pot as often as possible and pop cooldowns as many times as possible.
Warrior's spell reflect can be pretty damn good in some instances. You should look up where it can be used as an insane boost to DPS. Shockwave is also gonna be an invaluable tool if your group lacks aoe stuns. I highly doubt warriors are the worst CM tanks overall.
Got a friend to tank. Now we are Blood DK + Arms + HPala.
Hooked up with 2 Blance druids from the tool and done Auchindoun in amazing 39 minutes
Less stupid fails and gold looks doable.