Sending a reference/VFX plate to a compositor — OpenEXR
or DPX, whichever they ask for. Default to EXR + ACEScg if
they haven't specified.
General post-house delivery, no other instructions —
CineForm 422, Display (Rec.709). This is a safe
default most facilities can open.
Need real alpha in a video-package deliverable —
CineForm 444 Alpha, or Uncompressed
4:4:4:4 Alpha, depending on what the recipient can open.
Zero compromise on fidelity, don't care about file size —
Uncompressed, or EXR/DPX sequences with None/lossless compression.
Web/social delivery — H.264 for maximum compatibility,
H.265 or AV1 for smaller files if you know the
platform supports them, WebM if you need transparency in
a browser.
Quick internal review, file size matters most —
JPEG Sequence, or H.264/H.265 at Draft/Preview quality.