I use acrylic for blocking-in because they dry fast allowing me to move on to the detail layers in oils. I only thin my acrylic paint with water to make them apply smoothly and often just a small amount is all that is needed. I try to apply my acrylic paint thinly and smoothly with no brush strokes. Some colours and manufacturers paint might require two coats to get good coverage. I have used and enjoy Winsor and Newton acrylics but I have other brands too. I enjoy blocking-in in oils, but have learned to use acrylics to help speed-up my process to the finished painting.