If you play a Horde character and you like to get your XP in dungeons, the following Horde leveling dungeons should be on your list:
Stratholme. Back in the day, this instance was really difficult to complete. I remember dying many times here with my shaman. Nowadays, things are much easier. Even the instance has been divided in two parts. The mobs inside have also been adjusted, they’re now in a level range between 47 and 51. However, both parts of Stratholme are great areas to get XP because the NPCs at the entrance give you many quests. Also, from boss to boss, there are many packs of trash mobs to eliminate. In the “Live” side you can also get Righteous Orbs, materials for the Crusader enchantment which are still worth some nice gold and sell like hot cakes.
Blackrock Depths. It’s one of the Horde leveling dungeons that must be on your dungeon leveling path from level 51 up to level 55 or so. There are so many trash mobs in here so your XP rate will go through the roof if you’re going to be in a fast group. Not just the trash mobs are going to bring you the XP that you need, there are also many quests in Blackrock Depths, about 20 in number, but you don’t pick them all from the NPCs inside.
As I said, these should be two of the Horde leveling dungeons on your list if you’re going to XP this way. Also, a nice tip for dungeon leveling regards your talent specialization. If you character can be a tank, than train and equip it to fulfil this role. Things go much faster in an instance when you’re the tank.