Actually, you can go with anyone of these. Both has own pros and cons.
We can have more variety and design/themes in wallpapers. As you know that, we cannot have those in Paint. Paints have very limited types of textures. However, wallpapers installation requires experts. One more point is to consider is quality variations in wallpapers.
We cannot use wallpapers and paint both on damped wall.
If you want different themes then you can go with wallpaper otherwise, you can go with paint.