Generally I pick up all quests I come across. Group them by area and go to town. If I'm leveling too fast and things are starting to go yellow and green too fast, the collection quests are the first to be dropped and ignored, but I by no means outright avoid any quest. Well, except ones that have me doing too much running around. The pike one from STV {horde} that sends you to Arathi, Linkin's, stuff like that I pass on. The XP is just not worth running back and forth between continents and between a dozen different zones.