optimal transcoding format (3d viewport and VSE)? 1080p workspace. Not sure if I use the correct words or not to describe things, bear with me.

Due to pc limitations I need to render out a project in the VSE premature so its easier to deal with. The original footage is 8 bit h.264. Additionally I need to render out a particle effect I made in the 3d Viewport before adding it to the VSE project

I need to be able to re-render the output a couple of times (1-3) and not get artifacts.

I had been using 16 bit PNG for both the vse and 3d viewport. And this fulfills the requirements I think. 

I'm wondering if there is a higher format I should consider, or a lower format that fulfills the duty but is more savvy on space. Ultimately the project will be rendered out h.264 and get artifacts, just I need a format for the editing stage that won't increase these artifacts anymore than they have to be.
OpenEXR for a multitude of reasons. Half EXR is superior in every way compared to every other format if you are [intra | inter] pipeline at equivalent bit depth.