I hopped all over the place in the low 40's. I hit Dustwallow Marsh first and did about 8 quests there, I also hit Feralis, Tanaris, Badlands, Swamp Of Sorrows for a couple quests. In the late 40's be sure to hit Azshara for the two kill quests as well as the tablet collection quest that nets a ton of exp. I did hit stranglethron for a couple quests out of booty bay that involved the pirates and killing the one elite right out of booty bay but outside of maybe 3 quests I avoided it completely. Then when you are closing in on 50 you will want to hit the holy grail of multiboxing RAF leveling and head to Hinterlands.