Between the 14 and the 20: the 20mm/1.7 if you can find it for a good price. Otherwise, the 14/2.8 is also very nice, but it just needs a little more light. Depending on where you usually have your camera, this could make a big difference.
I fully disagree with only having the 45-200. At minimal zoom it is unwieldy close range, and it is quite slow. Its physical size negates all the fun of micro 4/3s cameras. If you want some telephoto, check out the 14-45 (or the 14-42 (not as good)), or the 14-140, which is again a big lens and quite pricey.
btw: I have a GF1 with the 20mm, 14-45 and 45-200. Approximate usage: 20mm: 80%, 14-45: 15% (much more on sunny days), 45-200: 5%.
If "I" could only have 1 lens it would be a 45-200.
I think most people would be more inclined to use the 20mm f1.7 as a very good low light lens, with enough focal length to do most of the more common photos like portraits and landscapes, etc. With a Panasonic you can also extend it from 40mm to 60mm to 80mm by using the EZ/ETC feature.
A 14mm would really limit you to wide angle shots only. I wouldn't want to rely on it as my "only" lens.
A 14-42 or 14-45 might be a better choice for the G/GH series, but the compact EP's and GF's seem to conform to the 20mm better.
Small camera deserves small lens. This 20mm wide aperture fits much of the standard lens features when a lens was packaged with a camera - old days now. I use it much of the time. But that does not mean I would not use a moderate telephoto too, but not a slow zoom thank you...I crop you see. I am using the Zuiko ED 50mm with an adapter, 4/3 to micro 4/3. Hard to go wrong on this optic as an all around normal lens, with any micro camera. You do not have to have image stabilization, shoot at a fast shutter speed. My favorite current lens. What else is there to add....35mm Leica Summicron is a good approximation at three or four times cost, but and equivalent of 40mm is close enough for under four bills.