Both work. The Speedy famously works with all configurations pretty well. something about the symmetry and design. So in that sense that's a winner for me. But the seamster also works well but it's more of an acquired taste. I wear both my SMPc and my PO's on Nato's often.
The contrast is more subdued in person. The case is titanium which looks really good with the grey. Putting it on the speedy is classic though.