Heroic Hierarchy

What's the hardest heroic instance? What's the easiest? Which one should I do first?
All excellent questions.

I can only share what I know about these instances.

Hellfire Citadel: The only heroic I've attempted is Hellfire Ramparts. This seemed like a pretty straight-forward instance. Nothing too funky going on and no real changes to the fights. If you know regular Ramps and expect it to be the same (albeit with harder hitting mobs) you won't be far off. I've heard Blood Furnace is fairly easy if you have a warlock for CC. Shattered Halls is supposed to be hard.

Coilfang Reservoir: I've been in both Slave Pens and Underbog. I don't find either of them hard. Some pulls get ugly as mobs can be immune to CC. I've even finished Slave Pens where the last druid died and we didn't get the buff. Steamvault is supposed to be hard with a warrior tank, easier otherwise.

Auchindoun: My first heroic attempt ever was Mana Tombs. What a mistake. MT was hard, hard, hard, hard! I ended up spending a fortune on pots and shadow resist for the first boss. By the time we worked up to final boss, we realized we didn't have the DPS to finish. Very disappointing. I've also been in Sethekk Halls but only briefly. My group fell apart somewhere in the neighborhood of the first boss. I've heard Auchenai Crypts is super easy and Shadow Labyrinth is hard.

Tempest Keep: Mechanar and Botanica I've found to be badge piñatas. First boss is just a FUN fight on heroic. Second boss in Mechanar used to be skipped but I've heard she got the nerf. Third boss in Botanica was also skipped two times I was in there. The last time I was in there, the first boss wiped us a couple times with an increasing Arcane Devastation. After about 3 wipes, it stopped increasing and just started out hitting the tank for 4-5K Arcane Damage. We called it. Never been to Arcatraz but supposed to be more long and boring than hard.

Caverns of Time: I've attempted Old Hillsbrad. The patrols with one humanoid and a dog spawned two non CC-able adds. So, um, yeah. It sucked. Bad. I can't even imagine what Black Morass must be like. It seems like sort of a spin on the wipe wheel unless you're group is really good anyway, so I can't imagine it harder.