I say this because the broadcast media, i.e. television or computer screen, is in the horizontal format. The video will take up a much larger area of the display.
For still photography use whichever fits the subject. A full length picture of a person should look better in the portrait or vertical crop because a tall subject will take up more more of the image area. Just don't put the face in the middle, put it in the top 1/3. A sweeping landscape usually shows better in landscape or horizontal framing (hmmm, wonder why they call it 'landscape'

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