I've never been up myself, but here is what I could find...
There are multiple routes listed as Class 3, but most of them involve glacier travel. The West Slope is listed as Class 2, technically easier but I prefer Class 3 as opposed to Class 2. Here's what Secor says:
"West Slope. Class 2
. First ascent and Floyd Burnette. Go south from Lake Catherine to the outlet of the southernmost lake of the Ritter Lakes. Follow the eastern shore of this lake toward the south, past the first talus fan and around a low buttress to the second talus fan. Ascend this fan (a real slog) to the upper bowl. Traverse right to a chute; be sure to enter the chute about halfway up, and not from its bottom. This chute leads to another talus fan, which leads to another chute. Climb this chute until about you are 50–75 feet below its top. Traverse left and up to the top of the ridge, which is followed to the summit. The top of this upper chute is difficult to find during descent." - High Sierra Peaks, Passes, and Trails
Here is an image of the West Slope, image taken from this Stanford EDU
And Secor says of Banner:
"From Ritter-Banner Saddle. Class 2. First ascent August 26, 1883, by Willard D. Johnson and John Miller. First winter ascent March 1, 1939, by Chester L. Errett, Bob Brinton, and Lloyd Warner. This route is class 2 from Lake Catherine; there is a class 3 section when approaching the saddle from the east. Banner Peak is a talus slog from the saddle." - High Sierra Peaks, Passes, and Trails
Secor also lists a viable Class 3 route up Ritter from Ritter-Banner Saddle. Might be a more natural route if you're fine on Class 3