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Anyone using thumb holes as a reason needs to consider what happens to their precious thumbs when they are in an accident and the wheels hit a gutter/hard object. Never stick your thumb through the wheel. Any off roader can tell you that too.
10-4 gives great high speed response but can get tiring on a long haul.
8-4 gives extra stability at the expense of speed of response. Great for trucks and buses as well.
9-3 gives no extra leverage in practice. In fact it reduces leverage. If you started at the 9-3 you started at the peak leverage and its all down hill from there. You lose the approach high of the leverage curve. So less than 1/16 of a turn later and you lost your leverage advantage. Starting at either 8-4 or 10-2 will allow you to get ride the peak twice as long. Not sure how much anyone can avoid in under 1/16 of a turn. To top it off its the most tiring position of them all.

The correct way to turn a wheel is a push pull system. Push with one hand while the other slides and waits. Then pull while the other goes back to a new position. You get near continuous turning that way and both hands are always ready to grip if required.
The use of a thumb hole/indentation negates this style as well.

I recommend the 10-2 for normal driving. I switch to the 8-4 when there is heavy wind.
There is no one perfect hold for any condition so practice all.
Even the 9-3 is useful if you are going off road, straight and are in heavy rutted tracks.