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.
The O75 was the reason I sold all my Canon gear and made the final leap to Oly (before that I had two systems, Canon FF for non-travel, Oly for travel).
And yet...my suggestion is Sigma 56. Yes, it's THAT good. I love my O75, but the Sigma is sharper at 1.4 than the Oly is at 1.8, and it's fun to play with! It's also cheaper and smaller and lighter. Especially with Xmas lights coming up...the 56 would be fun!
EDIT: Also, I've owned a couple of copies of the 45...it's okay. It was my first Oly prime, and I used the heck out of it. But it doesn't come anywhere close to the Sigma 56. As soon as I got the Sigma, I sold the 45 immediately.