Linelle, It basically comes down to what material they have and what you want. In my previous house I had black marble tile and loved it. When we built this house, I was going to do the same thing but my fabricators were out of the tile. They simply fabricated from a marble slab exactly as you described above-3 pieces. However, the price difference went from $ to $$$! It is more custom and I guess you could say "historical" looking, but honestly the other way gave almost the same effect to anyone casually glancing at my fireplace.

Weather White Oak

You have a modern rustic home and force-fitting a Spanish colonial look onto it will be a mismatch at best. I'd get rid of that traditional mantle and go with a simple beam-type mantle shelf instead. Keep all the decor super simple and clean-lined. And perhaps get some brighter throw pillows to put on that built-in bench. If I were you, I'd paint out that wood slat wall and all the trim to a warm white to brighten up the space. Feels a little cave-like and dark at the moment. Some inspo photos:

Contact wall paper will not hold up around the fireplace due to heat. It is also a combustible material, so would not be safe. That is a beautiful granite you have there. Understandable that you may not like it, but we cannot see how it plays out with the rest of the room. Please step back about 10 feet from the fireplace and take a picture so we can see the whole thing floor to ceiling and get the context. Some pictures showing the entire room and the furnishings are always helpful as well. If the main picture looks something like the one below, some of us can create some mockups to show how various recommended treatments might work. Try to get the fireplace opening as square as possible in the picture.