I've ran both 5x blood DK and a trinity melee team consisting of a Prot pally, MW monk and 3 frost DKS (or 2 frost DKs and 1 enhancement shaman at times) and found relative success with both.

All tanks is definitely the easy way to go until about M+ 8-ish since they can ignore a lot of mechanics and still have adequate DPS to down bosses. On trash pulls they are vastly superior due to the added stability and not being all that far behind on AOE DPS. The trinity teams shine in burning bosses down faster but require more attention to avoiding bad stuff or you will just get blown up.

For questing both would do fine. I did however find it annoying to quest as all unholy DKs since you really lack self/off heals, meaning you either constantly need to eat food or have the foof buff that heals you while out of combat up at all times, which became a pain when you randomly lose a toon here and there.