I think the quests are great at lower levels.
From around 20 or so tho, I tend to grind.
On my newest alt, a 35 druid atm, grinding makes sense to me at least. One way may be easier to you, but to me easy means not paying much attention.
So, I can kill a mob that is a level or two above me, and I have to focus some. Lets say this mob gives me 300 xp. (and I have to pay
some attention).
Now, if I grind one a mob thats a level or two below me, its preety much auto-attack, and shift form to heal every 3-4th one. Theese may only give me say 175-200xp each, but I barely have to watch the screen. With no downtime (and no worries and little concentration I might add) I can plow through theese.
This "mindless" grinding went super fast on my Hunter as well, I bet it would go fast on a warrior also. MY priest was much more "hands on" as death from even a add 2 levels below me could mean death quick if I was not paying attention.
So while my druid is killing a mob, I can stand up and flip the grilled cheese I was making, or take the clothes from the washer and throw them in the dryer, feed the dog, ect. Come back, click the next mob, then walk away again.
Thats what I like to do, say in the morning when most people are not on, and there is nothing going on withing guild chat, ect. And, if a random mob aggros you (and it's a level or two below you) you can take a few hits before you have to worry. So for me (and my playstyle) grinding works best, on stuff a level or two below my current level.
I am currently in the Shimmering Flats, grinding on turtles levels 31-35. (No poison attack, dont hit too hard, are yellow so they dont aggro YOU, and best of all, they dont run away when facing low HP like some mobs do, the stand right there (like good little mobs) and die.
Also, the first characters I played I spent alot of time wandering around looking for the locations the quest specifiy. So if its a quest I know where I know it already I'll do it, but the ones that make you hike, and search are slow in the proccess. They can be fun, but not on your 18th toon, lol.
Just my two cents.