Fast focus is a feature where you have a dial on the eyepiece where you can quickly adjust the reticle focus. Personally of the three mentioned, I would not consider the Rifleman, due to other 2 having better optical coatings. So between the VX-I and the Elite 3200, it would be a tough choice. Things to consider is the Elite 3200 has 1/4" click adjustments and the rainguard feature, where the VX-I has 1/4" Micro-friction adjustments and a longer eye relief than the Bushnell.