Of the three I own this one's easy. Between the Panasonic Leica 45mm f2.8, Panasonic Lumix G Leica Summilux 25mm f1.4 and the Lumix G 20mm f1.7, the 20mm f1.7 is my go-to lens.
The 45 may be a great portrait lens but I don't do much portrait shooting. It's also a noted macro but I feel the 20 (for me anyway) works fine for close-ups. When using the 45 for a macro I find it's DOF is overly narrow (for any given aperture) and often miss my focal point in the split second between auto focus and shutter release. Perhaps if I used it more I'd remember to stop down the aperture more than I normally would. And yes, if you're hauling a tripod it's not necessarily an issue but I don't always want to do that. I'm more of a shoot and run photog over the person who takes a long time staging. A.D.D. I suppose. There's always adjusting DOF after viewing a test image but "oh look at that other pretty flower".
The 20 is small, light and fast. Can't argue with that. Second the additional 5mm over the 25 makes it more versatile without adding much distortion that can come with wider lenses. Bonus, it's plenty sharp.
Since getting the M1 and shortly thereafter the Zuiko 12-40 I've been spending more time with the 12-40. But the 20 will always be with me. I did mention it's small and light.