If you’re questioning whether you want to play a certain class and have to come to the forums asking whether you should do it or not… Then that class isn’t for you.
You obviously want to play a Warlock, so play a Warlock.
“I like the Druid, but I think it will be a bad decision. This other class that I like better though might be a better choice… Do you think I should play the Druid or the class that I want to play?”
Kind of what this post sounds like. Kind of seems like you’ve made your mind up already.
If you’re asking the forums about how each class plays, then that means you’re not at a stage in the game where it’s going to matter. Play the class you enjoy, and enjoy it. You’re not going to be min/maxing and doing top tier content, so which class hits slightly harder isn’t a concern for you. Play the one that looks and feels cooler.
If you want actual answers to your questions instead of “Play the class you prefer”. Here’s what I got for you.
Warlocks have pets. Pets can tank. Non-Guardian Druids don’t make good tanks. Period. They can hold aggro for a minute, but are very squishy and don’t last as tanks. Warlock pets can be healed by healers and their Warlock. Warlocks also supply Health Stones, Soul Stones, and Summons. Druids can combat rez as well, but a Warlock can put it on a tank or healer before the fight any not have to worry about it.
Warlocks have consistently been good at pvp. One of their specs will always dominate. If you’re mostly interested in Boomkin, and Destruction, I would say Warlock. Warlocks can sit in the back and nuke people. Not to mention fear is extremely handy. They also have access to a teleport spell which is nice. (Although Druids do have the root/snare removal which is REALLY nice.)
As for rotation, I would say Druid is more dynamic. They focus more on procs, and what is useful right now rather than 1,2,2,2,3,2,2,2,3… Like a Warlock would. Warlocks build up Soul Stones, and use them for their heavy hitting spells. Druids don’t have to worry about not having resources (they build it really quickly compared to Warlocks) and have a lot more proc abilities. I personally find Druids to be more fun.