Out of those, my two favourite lenses are the Sigma 56 and the Oly 75. Up until I got the Sigma, the Oly 75 was my all-time favourite lens (not just m4/3...but any system I've ever used). I absolutely love the focal length, it's small and light, sharp, has beautiful bokeh, etc.
Then I got the Sigma 56...and wow. I haven't used the 75 since, and I'm actually thinking of selling the Oly lens. The Sigma is unreal sharp. Right from 1.4, it's crisp with beautiful colours and contrast. That, and of course, beautiful bokeh, and low light performance. If it was a little longer FL, I'd sell the 75 in a flash...the Sigma is THAT good. Pick up either one, and you'll love it!!
EDIT: I also used to have the 45 1.8, but sold it as soon as I got the Sigma 56...I can see using my 75 for street photography, even with the 56 in my bag, but I can't see myself ever using the 45 when the 56 is also at hand.