I have the 7-14 and the Nikkon 14-24.
I like the 7-14 better since it is so small, light and doesn't flare as easily as the 14-24.
It's a super lens and when you shoot in raw or jpeg (at least with a Panasonic body), the lens corrections are automatic. I haven't seen much curvilinear distortion for the year I've now used it.