9mm vs. 12mm is a huge difference, compositionally, and two stops is huge in terms of flexibility. Weights and size are close, while the build quality and controls favor the 12.
If your desire is sweeping landscapes and the forced perspective you can get with an ultrawide, then you'll have a blast with the zoom. 12 (24 eq) was once considered very wide, now it's easily reached by "standard" zooms so we're more accustomed to seeing shots in its perspective.
I don't own either and am just now considering jumping into µ4/3, but would probably save my nickels and get the Lumix 7-14. I have a 4/3 7-14 and it's a fantastic tool, a dazzling lens unmatched by anything else. That said, I could easily foresee the 12/2.0 as a "standard" lens. I once shot an SLR with 25/2.8 and loved the combo. That translates to 12.5mm in 4/3. The 45/1.8 is probably my only "must have" µ4/3 lens.
Probably just muddying the waters.