Have the Nikkor 14-24 and the Panasonic 7-14. The latter has less issues other than the purple ghosting in certain situations. I haven't used either of the new fixed 20mm or 24mm lenses but that 20mm looks pretty nice! My old 20/3.5 AI-S was known for its pretty good behavior in its day and I'll guess the same for the two, new 1.8 wides.
In any case, the 14-24 flares and ghosts like mad, even with the sun behind but not quite as bad with a carefully-placed sun in the frame. I simply use my hand or my hat in those situations.