Hello! On a MacBook Air, I would recommend not pushing settings too far. However here are the settings I use with my MacBook Pro in order to achieve decent looking video:
OUTPUT -> RECORDING:
Video Bitrate: 64000 Kbps (possible to use 128000)
Keyframe Interval: 2
Format: MXF (I would recommend mp4. I just use MXF because it works better with my editing software)
Video Encoder: Default
VIDEO:
Resolution: 1920x1080
Framerate: 59.94fps (not 60fps. Using true 60 will cause issues with audio in longer recordings)
Downscale Filter: Lanczos (Sharpened Scaling, 36 Samples)
ADVANCED:
Color Format: NV12
Color Space: rec709 (might be called just 709)
Color Range: Full
Again, depending on your machine, some of these specs will need to be lowered. The things that will make the video look the best are the 64000 bitrate, rec709 color, and the Lanczos Downscaling Filter. If possible, try to keep those numbers up. However they may need to be lowered and adjusted accordingly.
If anyone else wishes to recommend some other settings, please do so. I've been using these settings for a long time and have had nothing but good experiences with them. Its efficient and also makes a good image.
Hopefully this helps!