I've been looking for a while to find a place to quest at level 88 as Alliance.
I'd say the best Place to level from 88-89 is the Kun-Lai Summit
Why? Let me tell you:
Recently Blizzard lowered the amount of experience needed from 85 to 90 by a huge amount. So you will reach a higher level than before if you stay in a certain zone for longer than it's actually meant to be. It's also a good thing to continue with these quests although you've already "outleveled" it. Let me explain why:
If you are questing at lower level zones you will gain a little less experience, but at the same time you will do the quests a lot faster. This is especially true for Pandaria. The health of enemies is increasing by a huge amount for every level they gain, but the experience you gain from killing them or doing quests that require to fight them doesn't go up that much. This means you should quest in regions that you actually already are too "high" for.
Another thing are the mobs in MOP. You have the Mogu who have more HP than the average trash mob and The Mantis which are basically the new murlocs (You pull one, you pull the whole map). You should avoid doing quests which require you to kill a lot of Mantis. Of course at some point you will have to do them, but focus on Non-Kill Quests first.
Now with these things said I'd say the best way to level from 85-90 is:
Leveling Zones from Level 85 to 90 are the same for Alliance and Horde:
A more detailed list is here.