I prefer a very smooth surface for the detailed paintings I do. When I have painted on canvas, I purchased the smoother weave canvas that was portrait quality. Either cotton or linen canvas will work equally well for this technique. I tend to use different sizes for my paintings believing that some paintings are best in a square format while others appear best in a rectangular one. However, I typically use Anpersand Smooth Surface panels, which are great because they do not require any preperation before use. If you are interested in cutting an MDF panel to a particular size that you desire, I have a video that demonstrates how to prepare an MDF panel for painting here.