Be careful choosing a seat in the front of the "second" cabin. Depending on how they modify the galley by the door, you could end up with plenty of legroom. HOWEVER, don't plan on putting stuff in the bins above your head. There is no bin over fist row (just magazines/emergency equip IIRC). To be safe, you need to go back a few rows. In coach in the normal DL 757, I prefer second emergency exit row (it reclines). Would assume would be the case on Song too.
marc