Tough question to answer. First of all, a 20x20 garage is not very big so the size of vehicle/s you have will have a significant impact on bench and equipment location. (Builders that build "2 car" garages less than 24x24 should be shot.)
For instance, one of my farms has a 20' deep x 22' wide garage and I have an F150 extended cab pickup. That truck will JUST fit in the 20' deep garage ... another coat of paint on the bumper and it won't fit! So, if you have a full size pickup, the bench isn't going to fit at the end of the garage. Where is the mandoor? Got a water heater in the garage? Etc., etc.
Based on your locations ... S. California and VA ... may make a difference. In CA you may want the bench near the O/H door as the weather is nice and you may like working outside, but in VA, if you are in the western part, you may want the bench away from the O/H door where it is warmer in the winter. If you keep all of your tools in a large tool box/chest you'll want to arrange things so the tools are readily accessible from the bench as well as the engine compartment. I personally like my main bench near the back of the garage.
Best approach is to draw scale models of the garage floor plan, your proposed bench, and any other equipment you hope to add. Then start moving things around on your drawing to see what works out best. Think about how you work and how you will be moving around in your garage ... similar to how one would design a kitchen layout where a "work triangle" (sink - stove - frig) is critical.