I paint pet portraits in artists soft pastel, my preferred brand is Unison, they are quite simply the best I have ever used, though brands like Daler Rowney, Schminke, Sennellier and Rembrandt are all excellent. I find pastel superb for rendering fur and feathers and love working in the medium. Some artists like to work solely with pastel pencils but I only use these for detailing round the eyes and sometimes for whiskers, it is however surprising how much detail can be rendered with just the sticks of pastel. I would recommend a starter set from the Unison range and gradually build your pallette to suit your subject area or you could create your own starter set just for pet portraits. Artists Soft Pastels are a joy to use and once you have started on the pastel road you will be smitten!