My experience with a druid team so far compared to a Pally and DK team:

Pros:
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1. Stampeding roar is awesome. Nothing comparable in the pally or DK toolkit. Should be invaluable in Mythic+ chest runs.
2. Swipe is free *massive* AoE damage and very forgiving of targeting, which is a nice bonus when boxing.
3. Superior magic damage protection.
4. Incapacitating Roar has great range (talented) when you multi-pull large packs.
5. All one class (for class halls etc.) like pallies. DKs need a pally healer which makes it a bit more work.
6. Having one as resto gives you very mobile heals. Again, very nice for boxing.

Cons:
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1. Their heals are pitiful compared to the pally Light / Hand of the Protector so you need a dedicated healer. Hand of the Protector is simply OP and I don't think any other class can match it.
2. They seem to take more damage, but I suspect this is just a gear thing because they are apparently one of the better mitigators w/ larger health pools once geared up.
3. Managing their mitigation takes more finesse than pallies or DKs, which is extra hard if you're running 5.
4. Blinding Light not breaking on holy damage makes it superior to Incapacitating Roar.
5. No Blood Elf racial silence. War Stomp seems decent, but the windup time makes it annoying.
6. Having one resto kind of sucks. It impacts your trash damage (single target resto can perform OK damage though), and the biggest problem is their squishiness. It's also my resto that's in trouble. I may want to run with a prot pally healer instead of a resto druid for ease of placement.


TLDR; They have a harder rotation / mitigation strategy to manage, can't touch prot pally heals, but have an awesome mobility cooldown x 5 with stampeding roar.

Unless prot pally healing gets a big nerf, I can't see any other comps beating them. Druids certainly seem viable though.