Very different playstyles. Druid has most utility since you can spec 4 (four!) ways and fill any role. Warlock is a good solo class and pets lets you take on things and sometimes even cheese mechanics. Priest also has some decent utility since healers are always in short supply.
I have every class at 100, but it's never a bad idea to have a fully leveled druid. Pick the playstyle that is most fun for you since that's the point of the game! I don't like feral dps and prefer ranged classes. But that's just my personal preference. Which is why I'll use my druid more as a tank than dps.
Professions wise, if you are looking for profit, you can go 2x gather or 1xgather/1xcrafting. You can also choose the profession that suits your main class.
I personally love engineering for the toys and quality of life items (ie: Bank, repairs, mailbox, gliders, speed boosts, etc).