As I went through the process of looking for a prime for my OM-D, I realised that my options were limited to :
– Pana 20mm F1.7 (US$ 350)
– Olympus 17mm F1.8 ($ 499)
– Sigma 19mm F2.8 ($ 150)
The pana was a reputed lens. Sharp and fast, the lens did not perform optimally on a Oly. Key challenges being slow autofocus and banding issue. Then there was the long awaited Olympus 17mm F1.8. A well build, good looking, fast focussing lens, although a trifle expensive. After looking through a lot of reviews, two things became very clear – sharpness was not as good as the pana; and more importantly, the lens was not weather sealed. At that price, the Oly, without weather sealing and less sharp than a $ 350 lens was not exactly something that got me excited.
At this point in time, I heard about the Sigma 19mm F2.8. This lens was retailing at around $150 around christmas time. a quick review of the test results at various sites told me that the lens was pretty sharp on a m 4/3 and focussed pretty fast as well. Although the max aperture was F2.8 (one and half stop slower than the other options), but the price made me take a risk.
I have been using the lens for the last 3 months. Sharp enough for me ( i shoot streets not test charts) and very fast in focussing. There is zero shutter lag. The lens has not left my OM-D for the last three months.
One word of caution though, this lens & cam combination takes about 3 seconds to start up from the time you switch on the camera (indexing of the lens happens). So, a quick shot when your camera is switched off does not happen. Otherwise it performs well. The new version of the lens is expected in a fortnight. Hopefully, that would be even better
were
Indranil Saha (www.indranilsaha.com) 
You should try Pana 14mm f/2.5… A superb pancake and must be cheaper than the 20mm/1.7 🙂
Hello, I’m using the Pana 20mm F1.7 … I really like it but it is true that the autofocus is pretty slow when in low light conditions (especially compared to the Olympus 45mm F1.8 that I recently bought).