Though Considering the fact that Shingeki has less volumes and is a monthly is it safe to say that Shingeki is the most popular manga of 2013? Just saying numbers don't lie.
Snk won't see numbers this high again. Like the MF war, the excellent anime prompted people to buy old volumes in order to catch up. Things should normalize since the buying spree is likely over, and the anime is on halt.
If you look at the sales per volume list, from position 5 to 15 it's all old Snk volumes.