How is late game tanking and breakdown of each?

[TheForce]

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.

I gotta disagree about DRK being the most thoughtful to play. If we were talking about its HW or even its SB iteratiom, I would've agreed with you in a heartbeat. But now, there's a total of 3 whole skills that cost magic...with two of those skills being essentially the same move, just one being aoe, and one being single target. DRK really isn't the magic management Tank anymore, I'll give that title to PLD. We just have a greater amount of options for how to use magic, as well as more creative ways to use it and reasons to manage it (Requiescat is an example that comes to mind) which leads to more (and more fun, imo) magic management.

I have both DRK and PLD at 80, and honestly DRK is much easier than PLD. There's simply just less options, less freedom, and less complexity. Cannot speak on WAR or GNB yet though.