What I usually do is paint my models with acrylic paints. I used to use tamyia but I'm goig to give a try with vallejo acrylics. According to them, their acrylic paints for airbrush can stand washes with the most violent thinner I know...turpentine. For what I read acrylic paints should stand this attack but I had a bad experience with tamyia paints in this matter. Generally I paint the base coat, and then, for insurance, I spray a coat of acrylic matt varnish to protect the first layer of paint.
For washes I usually use oil colours, thinned down with turpentine. They take a while to dry but the final effect is great. At the first I tried painting with enamels and do the washings with acrylics. I got the felling that acrylics do look great after you wash but when they dry they become blotchy and very unrealistic. A few guys manage to get a good effect though.
This is my humble opinion. Take care.