I don't know which is more beautiful, the post or the pictures.

I'll go with watermark D. It's bold and precise, straight to the point, unlike the other watermarks it doesn't add any secondary colour to the photo, just the name and that's all they need to see.
The text (your company's name) is also in a single line without the bigger colour splash so it takes only a very little portion of the entire photo.

Lastly it's the most beautiful of them all and it's in black.