That's a good question. One of the different things about the Virtual Art Academy Apprentice Program that I built is that it does not recommend or teach any particular style. Instead I focus on teaching the underlying principles of all good paintings, whatever the style you choose. With the way the course is designed, you can paint as realistically or as abstract as you like. It makes no difference. 
This has the advantage of not limiting you to one particular style, and also of letting you follow and develop your own voice in painting.  A lot of online art schools don't do this, and the students all end up as clones of their teacher and never find their own expression.