Loregy has a great write-up on why the differences between the Emerald Dream and the Maelstrom, and ideally which of the two should be the next World of Warcraft Expansion.

There are two different camps of followers for the next WoW Expansion, the first group believes that the Maelstrom will be the next expansion (possibly with Azshara as the final boss), and the other group believes that the Emerald Dream will be the next expression (possibly with the Emerald Nightmare as the final boss).

The Maelstrom

Pros:

• Azshara is a perfectly reasonable boss inline with Sargeras as the end game boss
• The Maelstrom ties into the WoW lore of the Well of Eternity

Cons:

• Another World outside of Azeroth
• Maelstrom opens up the one and only portal to Sargeras’ homeworld (which doesn’t leave room for additional expansions, and leaves loose ends)

The Emerald Dream

Pros:

• Brings everyone back to good ‘ole Azeroth
• Backed by the new WoW lore book involving Malfurion Stormrage and further completes the entire World of Warcraft story

Cons:

• May not be enough content for a full expansion pack (possibly a new content patch instead?)
• Doesn’t tie in with unofficial reports and previously revealed WoW storyboard

So Maelstrom or Emerald Dream, which side are you on?