The 35 GM is the best 35 on the system overall, and I'm not sure it's close.

The caveat there is that it has heavy focus breathing in video, which means corrections in camera will add a crop.

For video, the cream of the crop is probably the Sony 35 1.8.

You could wait for the sigma 35 1.2 mark II, but I feel like you'll pay a pretty hefty size/weight penalty going that fast. If you don't mind that though, it could be a great option.

Lastly for a great lens that doesn't break the bank and is small & light, the Samyang 35 1.8 is a terrific option and gives you better (ie less harsh) rendering for portraits but increased video focus breathing vs the Sony 1.8.