My experience with rubber handles of any kind is that they are an inexpensive way for manufacturers to provide grip as a shortcut to proper design. Krayton provides a great grip by being very tacky. During long periods of hard use this has caused friction blisters on my hands, especially when they become wet with sweat. I have experienced this on knives, splitting mauls and other high stress tools. Almost always need to wear gloves to prevent this from happening. A properly designed handle will provide all the grip you need by nicely fitting you hand, not relying on the friction of the handle material.
Canvas micarta does indeed provide a firm grip and even becomes slightly tacky when wet. One of the best handles I have ever seen for a large knife is from the hands of Matt Lamey on my 7" Camp Bowie. Very secure and no hot spots or blistering problems whatsoever. Also much more durable than rubber.
If you have to rely on the handle material of a knife for grip, somebody really screwed up the design process.