World of Logs - Real Time Raid Analysis
Use this site to get a boss by boss look at what class is currently doing the most dps. I have linked the Firelands overview.
State of DPS
Is an aggregate of world of logs where they average out all the input to get overall rankings. I know nothing of the metrics or logic to how they gather this info so maybe take it with a grain of salt but it doesn't look that wonky.
But you still need to take into account where your character is at gearwise and what you are raiding.
For example, if you are rocking mainly ZA/ZG items and are a rogue, you should stick to Ass. But once you are mid-end Firelands and in T12, you will be several thousand DPS higher as combat.
But if you want the simple "which is the easiest class to sit there and pew pew" you will still have an easy time as a mage.
Hope this helps