I have a Chihuahua. If you have one or a dog of similar size, if they are going to sleep in it, get medium size. I bought the medium in pink (it’s Sparkie’s favorite color). She seems quite happy with it. I like it because the cover zips off for cleaning and is the right size. It also doesn’t have a sewn in cushion top that would keep it from being cleaned. My cat has been caught laying on it in the daytime so he gives his seal of approval also.