So, I started with the 12-35 on the GH3 thinking it's the perfect all around lens. It sort of is. Very sharp. Light. Compared to the Sigma lenses and Zeiss lenses it looks very sterile though. I started using the Sigma 18-35 when I could use a tripod and fell in love. When I needed to go handheld I just used a monopod. Now I use the Sigma almost 75% of the time.