50mm is a good "what you see is what you get" lens.
The 1.4 boken is tricky to use though. If you focus on the eyes, only the eyes and nose remain sharp. The rest of the face goes into a gradual soft focus.
My fav portrait lens would be the 85mm F1.2L prime. Otherwise for versatility the 70-200 F2.8L IS works well too.