When I leveled my DRK, it was more casually than anything else. I would do leveling roulette aND then go back on my DRG to do the 60 stuff and other dalies. Once I got back into the game I learned how great hw beast tribes were for EXP so I did all of those, leveling/50 roulettes, and occasionally did hunts. Got both AST and DRK up from 52 all the way to 60 just from this in about a month, and this is just cadually. Not a good way, but then again I did this so I wouldn't get burnt out.
For my other tanks I do a mix of fates, dungeons, and leves, though I hate tanking low level dungeons.