When I have to guide my clients with the process of decorating their walls with artwork or photography, they want to know what is the best layout.
To me everything depends on proportion. To create a well balanced gallery wall you have to do your math.
Of course there are some layout ideas to help you to create the perfect gallery wall, and you can combine different dimensions in some of them, but if these artworks or family photos are going to be above a furniture (sofa, bed, sideboard) you have to measure first the piece to make sure you the composition has the correct proportion.
Personally, I'm more minimalist and I like to add a big artwork to create more impact but keeping serene.
I'd like art, of course, and going to museums and galleries, but I always find chaotic too many artworks in the wall if the furniture below is already full.
So, when my clients ask me to add a wall gallery, I try to keep minimal and clean to create the harmony without losing interest.
Another thing that I like to do, and no many people agree, is to combine different styles mixing Abstract with Realism, landscapes (modern or traditional), etc.
In the image above from a past project, I combined a wall with layout with a wall with one big artwork. Also there are different styles, the layout wall is with family portraits while the one artwork is Modern Graphic.