I’m a long time altoholic. I’ve leveled each class from 1-60 in SL, gotten bored, and am doing it again.
Overall, druid is one of the best levelers in the game. They have a perma 130% move speed with Cat Form. Great for running out of indoor areas. Similarly, they have a sprint. They have stealth to easily get in and out of dense areas. They have excellent heals. They have a ranged pull (Moonfire). They have great AoE. They have decent single target. Above all, Travel Form gives you instant mounting. Flying in Travel Form also lets you loot objects (dead mobs, resources, quest objectives, etc) without unmounting!
All of this is available to each spec. It’s insane.
Here’s a breakdown of each spec while leveling:
Guardian - incredibly tanky, great AoE damge, and decent ST damage. Pull literally as many mobs as you can with Moonfire without them leashing, Thrash on CD, spam Swipe, and you win.
Restoration - not as tanky, but just as survivable as Guardian. Their base damage is higher than Feral and Balance, but there aren’t any spell interactions, so their overall DPS is lower. However, as most DPS specs don’t get those interactions until later in the leveling process, this makes Resto a great leveling spec early on. Specifically, going Balance or Feral affinity /w with the Master Shapeshift PvP talent makes for INSANE dps for a healer while leveling. Seriously, try it out.
Balance - excellent AoE, decent ST, but insane ST when cooldowns are up. Lots of tools for kiting and keeping enemies at range. However, I’ve found that using these tools really takes away from precious globals to kill mobs. This is especially noticeable since outdoor mobs are easy. They die in like, 10-15 seconds. If you’re spending 2-3 globals to kite, your kill speed increases nearly 50% per mob. For that reason, I don’t like Balance leveling.
Feral - no AoE for a while. Even when they get going, AoE is very lacking. ST is ok, but nothing special until much later levels. Unless talented, Moonfire can’t be used in Cat Form to range pull, so it’s more awkward to group up many mobs and AoE them down. Energy regen is slow until later levels as well, making the spec play slow. It’s not nearly as tanky or survivable as Guardian or Resto. Overall, this is Druid’s weakest leveling spec.
In conclusion, if your sole focus is easy and quick leveling, Guardian hands down. It’s not even close. Moonfire to round up as many mobs as possible, spam Thrash and Swipe, use your defensives liberally. Instantly mount up, fly to another quest area, rinse and repeat. You’ll feel slower in single target fights, but the ability to AoE makes up for it BIG time. There’s really no reason to swap specs, it’ll just slow you down.
If you’d like to play Balance in end-game though, that’s completely fine to level with. They’re great. Again, the base kit of druids makes them one of the best leveling class in the game. If your goal is to simply have fun, any spec will do. Personally, I have the most fun on Druid playing as Restoration with Feral Affinity. Managing DoTs between 2 forms (Moonfire, Sunfire, Rake, and Rip) while keeping HoTs on myself (Lifebloom, maybe a rejuv and regrowth) is just incredible fun. It feels far less punchy than something like a Fury Warrior, and more “maintenance” like an Affliction Warlock, but you’re constantly busy, you stay alive, and mobs die.