Were should i go to in World of Warcraft after level 27

Best location to go after level 27 depends on faction and gaming style.
For Eastern Kingdoms - I suggest Arathi Highlands if you have trouble with player vs. player. If you aren't worried about that then Hillsbrad Foothills and Stranglethorn Vale are very popular. For Kalimdor - I suggest Ashenvale and Thousand Needles.