Either Combat or Mut are viable. Mut can put up a much faster pace because its damage isn't dependent on cooldowns and VW leaves you at full energy after a kill while Combat relies on cooldowns and RB reducing cooldowns for damage and is nearly always empty on energy after a kill. Rupt multidotting with a defensive rolling is very good against multiple mobs too, and you can do it far more often than BF+KSp/AR.
Back when MoP launched, I leveled as Mut while all my competitors for Realm First 90 Rogue were Combat. I beat them by several hours, and spec seemed to be the only major difference. You can play as either spec just fine, but Combat's toolkit certainly isn't the "best" for leveling.