Petapixel tested all the best 24-70mm lenses and comes to the conclusion that the Panasonic L lens is the best performer. Still they recommend the also very good Sigma 24-70mm lens because of the much lower price:
Though the Lumix was most commonly my personal favorite out of each of the tests, I don’t know that I would say it’s the best purchase. If you recall, initially I said this was a test of sharpness vs price, and the Lumix is nearly twice as expensive as the Sigma.
Is the Lumix twice as good as the Sigma? That’s ultimately up to you to decide, but I personally don’t think it is. It’s definitely better, and I think if money were no issue I would select it over the field. But since money is always an issue, it’s hard to argue against the Sigma.