For desktop Raven quote, I think you could take advantage of how big the screen is. The text is centered so it is easily noticeable, but I doesn't have a strong relationship with background image as a postcard.
As for the mobile Raven, I like how the quote is on one corner and the person is at another corner. But I think there needs to be more distinction between the quote and the person. Your hierarchy suggests that the person is more important (judging by the font-size) rather than the quote. Is that intentional?
The Hound Desktop quote works very well with the background because the color and position is relative to the image.
As for the mobile version, I think you can make more distinction between the quote and the author because the whole thing is read as one quote. Try different size and weight here because it is not working as well as it did on desktop. There is a great white space in the top left quarter of this image, try utilizing that space.
Jon Snow desktop font size is too small. It feels that way because his face (similar shade of color as your type) is competing against the type. The author's name is getting lost in the background because it is too dim. There is a lot of great space around the face, try exploring those spaces.
For Snow mobile, I like this better because the text jumps out at me from the start. It still reads very well with the background image, and doesn't feel out of place. I think you could still make the author visible more.
In general, I think you could make the quote color whiter, so that I can see it clear against the blue/grey background. Try different typeface - the sans serif works well, but I think you could explore different types of sans serif and the weights as well.