They are a bit easier, but both are a hell of a lot easier to than, say, a warrior. Then again, my mage leveled really fast for me because I liked it so much. My rogue leveled a bit faster because I *had* to, but when I had no enthusiasm for it, it went really slow. Sometimes, it really depends on how much you like the class.
Though, also, I can't talk *too* much from experience because my mage/rogue aren't endgame, they're only 30/40.
Rogues have significant advantages over other classes with stealth. I can't tell you how easy it makes questing.
Mages kill really fast, but not usually as fast as a Rogue. Plus, when they're done killing really fast, they have to take a break to drink.
And also, this is my 9000th post. You should feel lucky! 
(hehe jk)
Haha. -_-
And, stealth makes things annoyingly easy. Have to kill the named at the end of the cave? Just stealth there, pop up, kill him, vanish, leave. Mage? Kill everything in the cave, and have sheep break every time you try and kill the named, so you get pounded into the dirt and mutilated like the clothy you are.
Though, mages are still my favorite class, simply because they do have other advantages that make life a lot easier (evocation, teleport/portal, water/food making, blink), but unfortunately, other classes take advantage of mages...
I do like hunter, though. You kill almost as fast as a rogue, are never really alone, and, hey, I can stealth! -_-
