I wanted your opinion on the lens market
Which of the two is best in quality to use it with lumix gh3
tamron 24-70 2.8 vc or Panasonic 12-35 2.8

First of all there is a big difference is focal length between both lenses, 12mm is much wider then 24mm so much depends on how wide you want the lens to be, second, I"m not sure if stabilization and autofocus will work on that tamron lens when you use it with the gh3? I do know the 12-35mm lens from Panasonic is excellent but you have to bear in mind you are locking yourself into a m4/3 system while the Tamron would be usable on other camerabrands I guess.

Who cares about other camera brands, GH3/4 ALL THE WAY!

On a more serious note, 24-70 will become 48-140, which, if the stabilization does not work, means you will NOT be able to shoot handheld, at all. Just something to keep in mind. With my newly acquired 12-35 I have shot handheld at both 12mm and at 35, and if you're careful and smooth enough, you won't need to stabilize it in post, it looks great.