I own both and my camera is a G1.
Perhaps I'm not a normal user but I very much prefer the Panasonic 25/1.4, or the PL25 for having a short swift name on that big and heavy lens. Cause big and heavy it is with the same size as a Sigma 50/1.4 for a FF camera...
The main reason for preferring the PL25 is the focus length. Some like a short normal better and then the G20 is the best lens. I like a normal normal, sometimes even a normal on the long side (like the old 55 and 58mm lenses). The second reason is the rendering which while not dramatically different from the pancake still is more to my taste. The third reason is the aperture ring which make the lens a better ergonomic choice, to me, than the pancake. Then there is the sheer size of it; the pancake is too small and manual focusing id fiddly. And yes, half a stop of speed is never wrong, just as the Nokton 25/0.95 is another stop (or at least 2/3 of a stop) faster again.
It's easy to list the advantages of the pancake though and I guess most users would mention border to border "sharpness", size, weight, price, coolness factor. Lol. For me it is just too small, too impractical and too boring and so it comes to use when traveling only.
Well, all that is more personal than convincing I guess.
regards,
Jonas