They both work quite well. As much of a fan I am of black wallpaper, I have to go with the other one. It gives a bit of a warmer atmosphere which I feel suits the theme of the room. But both work really well, so I can definetly see why you need help lol.
I like black bricks! I think you could bring the pop of blue into the room another way, like through decorations and wall-mounted items.
If you don't think you have a lot of blue items; I'll sometimes craft a few DIY items with the "customizable" icon just to see how the look changes. Sometimes an item I didn't think I'd care for is actually really cool in another color (like the bamboo wall decoration!)
I think I’m leaning more towards the blue simple-cloth wall because of your votes and the fact that it’s very similar to the wall in my IRL bedroom pictured below: