Sorry about the late reply...
I climbed Ritter from Lake Catherine many years ago, climbing to the Ritter/Banner saddle, then up a really steep chute. Would not recommend the route. I think Muir himself described it as hairy scary.
Several years ago, I climbed Banner from the same saddle, and it was more fun. Like the above says, class 2, with maybe a little bit of 3. Skirting the S. side of Catherine Lk was more "interesting". I recall I had crampons for that section as well as the long snow tongue from Catherine up to the saddle.
