Regardless of your spec of choice, leveling your rogue in Mists of Pandaria should be an enjoyable experience. I tend to enjoy combat's simple Sinister Strike-spamming playstyle for the leveling grind, but subtlety's amazing burst and assassination's potent poisons are more than powerful enough to get the job done. If you were lucky enough to acquire your Fangs of the Father, they'll carry you until level 88 or 89 with their awesome damage.
The first key to a swift leveling experience is to minimize your downtime. The less time you spend in combat, the longer it will take to hit 90. The second key is to increase your damage output. While our damage is already formidable, taking out targets faster is always a good thing. The third and final key is to eliminate the competition. If a member of the opposing faction is killing mobs in the same area that you are, you need to increase the supply of mobs by reducing the demand.