WAR - You wanna have the highest skill cap and put in twice as much effort to get to where other tanks are. Great for AoE pulls where you'll feel like an axe-wielding demigod. Single target is kinda 'eeh'.
PLD - Most straightforward, simple rotation. Your healer dies, you dgaf. You're your own healer.
GNB - New kid on the block. Is less about dealing with damage spikes and more about making sure they don't happen. Great OT, and the ST rotation feels super nice with Gnashing Fang and Continuation.
DRK - Has some niche CDs that frankly could be axed for something more useful. You'll find them by the buckets since they're the poster boy for ShB. Feels more thoughtful to play than other tanks due to having to balance defense and offense w/ your mana.