I've fired all three, if forced to make a final choice, I'd have to go with a FN-FAL, I own the SAR-48 from SA and have throughly enjoyed it for almost eleven years with no problems (insert fist knocking on wood!).
I fired the G3 when qualifying for my 'shooter's rope' and just plain didn't like the feel of the weapon, not one I would like to go into harm's way with.
The M-14, I'm of two mind's about; I have always love the Garand mechanism and my first choice is my trusty M-1, the magazine is nice, but I've always had issues with the muzzle jump on the -14.
Ah well, to each his own, I'm heading to the range tomorrow for some quality time with my M-1911A1 and M-1 Garand! Long Live the Dinosaurs!!!!