Reasons to prefer the 135 include 1) increased background blur at a given f/ number 2) greater reach 3) iq 4) build quality (in that order of importance for me).


IMO the iq and build quality of the 100 f/2 are easily good enough. And you've said 2) is not an issue. So unless you're looking for the absolute maximum possible background blur, I would say the 100mm will be fine.