Since i have the Pentax K-3 III I'am uploading video's again

Because the camera produces .mov files, I upload alsso .mov files.
In my video edit software (for now the simple free OpenShot editor) it is easy to convert it to .mp4.

If I take search the difference are
https://www.movavi.com/learning-portal/mov-vs-mp4.html

My guess is that .mp4 files will generate more sales.

Which file format do you use for uploading video?
And wich one is the best (for sales)?

Which file format do you use for uploading video?
And wich one is the best (for sales)?

Uploading in MOV, this container usually contains more information than MP4. Especially since your camera shoots in MOV. You don't need to specifically convert to MP4.
Movavi Video Converter converts lossy video and the MP4 container compresses the information a lot.
You only need to convert to MP4 if the file size is more than 4 GB (stocks usually don't accept anymore).