I do Tanaris from about 41+, there are lvl 50 mobs down at the bottom. Ungoro is not bad from 48-55. Just pick the quests you like to do or mobs you like to kill since you probably don't need them all. I love Felwood, since I know what is there, there is herbs, mining and Timbermaw rep to get through the cave. That is about 48-54. Winterspring is fun since I like snow. GREAT for mining, sucky for herbs. Mobs are about 54-59. I don't mind eastern plaguelands. Mobs are 54-59. Not great for mining since not a lot of nodes, but are high ones. I hated silithus, maybe cause I didn't know what I was doing. It just felt like it was full of mobs and crappy quests. Probably great for grinding out exp on mobs though (lvl 54-59). I sometimes go back and do quests that I missed or that I like, you still get pretty good exp for them. Also, might try to run a few instances, they always seem to be good for exp. ST (48-54), BRD (52-56-58), LBRS(54-58). Hope that helped, good luck.