For most people this seems like a silly question, some think, 'what difference does it make?'. For me, it makes a huge difference! If I am creating a very detailed painting I will use Oil paint. The reason for this being that oil paint has a more translucent ability which enables me to create many layers of color. Not much that we see has one color in it. It may appear to be one general color, but when looking deep, there are most often different color componenets. This gives me the real life quality. Another reason I like to work in oil, is the drying time. Unlike the acrylic, it can take several days and possibly even weeks to dry. Giving me the ability to work on several pieces at a time. My fine art is what I focus my time in oils into.
Acrylics are great for faster works. Most of the original paintings I sell in La Jolla are in acrylic. I have learned how to create an oil like look with the acrylic. There are times when I prefer working in this medium for sake of time! There are always those times when you need a project done fast, so it has been great to be able to use this medium to get my projects done on time.
My suggestion is to work with both, get a feel for them and see what you like best. Everyone has their own style and what they like to work with. So find what works for you! Happy Painting!