I use yellow split peas for soups like this because the color is so appealing. I tend to have better luck with bagged beans and split peas cooking evenly, rather than those kept in bulk bins. Lentils can be substituted for the split peas, and will take less time to cook through (these seem to be okay from bulk bins). Any type lentil will work, though choosing red or yellow lentils will keep the soup bright in color. Brown or green lentils are just as delicious, but give the soup a muddy appearance. Substitute hot Italian sausage or any link type sausage for all or part of the mild Italian sausage. If using precooked link sausage, slice into discs and brown in the same manner.