I don't have either of them leveled, but another thin you should consider is where you will be n the fight.

As a melee, you lose dps not only when the tank moves, but when the mob uses an AOE and you have to stop to dodge it. Smn gets full dps from all sides, and has several of its abilities instant cast, meaning you can use them even while dodging something.

That, and if you have a bad tank, your mnk will suck and it won't even be your fault.