I have experience with both cameras. They have similar sensor performance with perhaps a very slight edge to the S95. In terms of lens performance, the GRD III lens is
signficantly better at the edges/corners. My S95 had similar lens performance to my S90 (x 2 samples) which I pitted against the GRD lens
here.
The GRD III lens is good enough that the corners still look good with the 21mm equivalent converter (
examples).
All things considered, my answer to your question is that the final image quality at 28mm (equivalent) f/2 favors the Ricoh.
Other differences you probably already know:
- Canon has effective IS, GRD none.
- Canon zooms, GRD does not.
- Canon is significantly smaller/more pocketable than the Ricoh.
In terms of feel in the hand, controls, usability, there is no contest (Ricoh better).