@elianafranzenburg
Wow! What an amazing sunset!! My house is surrounded by trees and we live in a valley, so I rarely get to see sunsets or sunrises. :/
I’d brighten both photos – they strike me as being a bit dark.
I think there is a place for vertical photos of sunsets; I was recently designing a book and was constantly looking for vertical photos of all sorts of things for backgrounds to pages. If you were to make a vertical greeting card, you’d need a vertical photo. It depends on what you use your photos for. That being said, I’m liking the horizontal photo better – the point of a sunset is the sky, and that photo certainly showcases the sky much better. The vertical photo gives me the feeling of being “cropped in”. Maybe if it included the sun itself or something, it might be different…
Another thing to consider is your foreground – silhouettes can add a lot to photos like this. However, somehow the trees in these photos feel like they’re blocking the view instead of adding to it. If you have the chance to take this kind of photo again, think about how to use the trees or whatever’s in the foreground to enhance the photo, if possible. I know sometimes there’s just not much you can do as far as that goes, so you have to work with what you have. 🙂