By your title I can see you did not heard about the GX1, have a look.
From a general point of view the GF1 is more "loved" because it was the first, it was the news out on the world, it looked gorgeous and it had an amazing image quality for the first of it's kind. I own a GF1 and I would strip it of some functions, as they did in the GX1, still It's an amazing camera, portable and with a great performance.
In camera size/weigh between GF1, GF2 and GF3. The GF1 is the bigger and the heavier, GF2 significantly decreases sizes and GF3 even a bit more. Never had all the 3 in my hand to compare weight, but for the size of the camera (GF1) you would expect it to be lighter, but it isn't. I know that gf2 is lighter than the gf1.
The gf1 has no touch screen, gf2 and gf3 have, because of this panasonic stripped gf2 and the gf3 of some physical controls and for this reason the ones that loved gf1 didn't liked so much the gf2 and the gf3, finally as to external features the gf3 has not hot shoe, but since the external flash is not an issue to you, I guess you could discard this difference.
Relating to the gx1, is simply a fine evolution of the gf1, it has almost the same size as the gf1, the physical controls are back, although it also has the touch screen introduced in gf2 and the hot shoe back is back. The rubber grip that was introduced in it is very handy as well.
As to the features that this 4 panasonic hold, they are almost the same, the only things that I point out are:
- gf1 does 720p video and the rest does 1080p
- gf2 and gx1 can record stereo sound
- gx1 has a better sensor and a better image quality. Also it generates better jpg's.
Of course that there are more differences to refer to, you can check them here.
In this site you can find extensive reviews about the gf's and the gx1 and also of it's cousins from panasonic.
If you are pointing a bit more pro with the pictures you take, gf1 or gx1 would be the best options, they are also the bigger cameras, if not, if you're looking for a more simple approach to your photography gf2 or gf3 would suite just fine for you and of course they're the smaller cameras.