Both about the same in terms of performance. I have the Seidon 240m and like it.
With either of them, make sure your case can fit them. My first case with 2x120mm spots didn't fit as the spacing wasn't right. My second case, it fits, but I have to have the rad then the fans on top pulling the air out. Seems to work fine, but no way to fit a push-pull, or fit the fans first in a push config. I learned 2x120mm fan spacing does not mean one of these 2x120mm and the fans will fit properly.