For me, I like the 50/2 macro on the EM1 better. And on the EM5, I like the 45/1.8 better (since the lack of PDAF on the EM5 does not handle the 50/2 as well).
Both lenses are really good, although the 50/2 seems to me to be slightly sharper and have better subject isolation. In terms of optical performance at portrait distances, the 50/2 is as good as the 75/1.8, in case you are familiar with that lens. If you have to choose one over the other on the EM1, it comes down to size and speed. If the more compact size and focusing speed of the 45 is more important to you , then that is your lens. Otherwise, there is no other reason to choose it over the 50/2. The 50/2 is weather-sealed, so it is a no-brainer if you shoot mostly outdoors. And on the EM1, you can calibrate the PDAF to the 50/2 with its "micro-focus adjust" to give you extremely accurate and razor sharp images when using autofocus. If you prefer manual focus though, neither the 50 nor the 45 is as precise as a good manual lens (e.g., a Leica or Zeiss M lens).
Autofocus speed: the 50/2 can be slow when dramatically changing subject range. It can take up to two seconds to autofocus in low light when switching focus from macro distance to near infinity or vice versa. However, when shooting within a narrower focusing range, the focus is very fast.
Hope this helps you decide.