Paint thinner and Mineral Spirits are essentially the same thing and in fact if you look on the Paint Thinner can it's probably say; 100% mineral spirits...
I always choose Mineral Spirits because paint thinner can contain; Naphtha, Mineral Spirits, Acetone, Xylene, Turpentine, Toulene and MEK are all "paint thinners".
Mineral spirits are used full strength and never diluted...Mineral spirits is a petroleum based