This question comes up over and over again for me as an artist and educator. Why should I use oil instead of acrylic? Well, the short answer is, you cannot do the same things with acrylic as you can oil.
Acrylic paints are composed of pigments and glue. Artists, manufacturers, and scientists began using acrylic in order to complete works of art in shorter amounts of time. If you're looking for fast dry-time acrylic is the way to go. However there is a downside; you cannot get the same atmospheric clouds and diffused light as you can with oil.
Oil-based paint dries slower. However, it spreads out in a different way. The pigments dissolve into glazes. These glazes stick to the layers below in a different way than the glue pigments are suspended in acrylic do. You can dissolve these pigments into finer washes uses turpentine, and then spread them out on your two-dimensional surface. Clouds, mist, fog and anything that looks fuzzy are characteristic of artistic works using oil-paint.
Try working with layers of both acrylic and turpentine-diluted oil paints. It will change your drying time, and allow for you to depict atmospheric light and diffusion you could not before.