>>372656624-70 and 70-200 equivalent is wide enough range for 99% of work you'd do. These lenses, despite not having the Leica badge, are well built, super sharp, and marketed more towards prosumers. On a Panasonic body they utilize DFD which will give you slightly improved autofocus, and utilize Dual I.S.
Olympus's pro line has the 12-40mm 2.8 and 40-150mm 2.8. Both are larger, heavier, and more expensive than their Panasonic counterparts, but offer more reach on the tele end. You will not find IS on the Olympus lenses, as they rely on in-body IS.
I use the Panasonic 35-100mm f2.8 and find it very sharp wide open. I'm sure the 12-35mm is just as nice, but I shoot more on the tele end.
