Street Photography: Olympus 17mm F1.8 or Panasonic 25mm F1.4 ?

I don't know about neither as the PL 25 1.4 is one of the very best m43 lenses period.  The 17 1.8 is a better focal length for the street, but the 25 1.4 has significantly better IQ.

Based on the DPR EM5/17 1.8 combo samples, the 17 1.8 is an underwhelming lens that doesn't bring out the best of the EM5. The center is not spectacular and the corners look too weak for a wide angle lens that could be used in landscape/architecture photography and other applications where it's important to have even sharpness across the frame. But even at apertures like f4 where you'd expect even performance, the 17 1.8 fails to impress.  (See night image with ferris wheel in the DPR 17 1.8 preview samples).

People will talk about the AF performance of the 20 1.7, but it's more than adequate for street photography. I've seen some decent images from the 17 1.8, but even the best of them are not as crisp, color/contrast not as good as with the 20 1.7 or PL 25 1.4.

Sharpness is not everything, but when you consider that the 20 1.7 is only a few ticks less sharp in the center than the superb PL 25 1.4, it's clear that it's right up there with the best of m43.  This coupled with it's small size and good price make it pretty much a must have lens.

Mechanically and build wise the 17 1.8 is excellent.  But if images don't look as good as you'd get from some other lenses, I don't see the point.

For the price of the 17 1.8 plus the non-optional $90 lens hood, you could buy both the 14 2.5 (another lens that is loads sharper than the 17 1.8) and 20 1.7 and you'd have a killer 1-2 punch for street photography.  Note: you can find the excellent 14 2.5 from some Asian Ebay sellers for $150, which makes it a no-brainer.  For street photography, the wider the better, IMHO.

All that said, for your specific question without a doubt I'd buy the Panasonic/Leica 25 1.4 over the Olympus 17 1.8.  Plain and simple, it's a significantly better lens.  The border and corners of the PL 25 1.4 are sharper than the 17 1.8 is in the center!!!  (See Lenstip review of both lenses).

Good luck, Markus