I voted for the f/4 IS. It's optically excellent (better than either of the the non-IS versions), and the IS can be a big help, especially with portraits where the shutter speeds can get lower than easy hand-holding speeds at the long end. Note that I'm assuming outdoor sports and outdoor portraits. If you'll be using it indoors for either application, you'e be better off with a prime. The 85mm f/1.8 makes an excellent lens for indoor sports and tight portraits on a crop body, and is easy on the budget (one of the best values in the Canon lineup, IMO).