I have both Comnav and Garmin Autopilots on the same boat. I added the Garmin both for redundancy and because the Comnav would just not perform to my expectations (I had a Simrad on another boat and I trusted that one to steer me into Gig Harbor - with my hand near the controls!).
The Comnav is now strictly a backup unit (and rudder angle indicator). There is simply no comparison in their performance. The Garmin mostly keeps the crosstrack error less than ten or twenty feet, even with big cross currents. Unlike the Comnav it requires no adjusting and tunes itself to the conditions.
I believe that any of the major manufacturers (Simrad, Raymarine, and Furuno) have autopilots with similar smarts. In my opinion, the Comnav is just primitive by comparison.