Hard to say who he'll pick. The way I see it, the most likely ending is the open one, unfortunately.
Barring a timeskip, he won't choose Yakumo because she's Tenma's sister. He may choose Eri now, but once again Harima is capping it at a friend's level, despite her advances. I can't see him choose either girl within a quick frame of time, it would just feel wrong. Tenma (unfortunately) had that strong of an effect on him.