In both Mage/Rogue and spriest rogue the biggest thing to learn is how to set up resets for one another. You have to be very patient with this comp. If you don't score a kill in the opener, odds are that the other team will start on the mage, and the rogue needs to allow him to escape los and evo or eat. Likewise the mage needs to setup restealths for the rogue. Your kills should be planned a few minutes in advance. You should know when you will both have the cds and available cc to score a kill.
All three work good, but mage rogue is by far the best. Too many tools compared to the others and much better on demand burst. Shadow rogue works good, but really your priest will just tank forever and it's going to be a pain against a lot of setups. It does work though, just much easier done with a mage. Disc rogue is just not as strong.
Mage/Rogue is great till around 2k. Feral/priest just keyboard turn and just rape you. Shaman/x is fun too. DK/x is a joke, kill the dk in the opener everytime with good synergy. I think there are 10 teams total past 2.2k in the entire world.