The size of the automatic wire stripper itself varies only minimally, if at all. The most important thing is that they fit well in your hand and that you can work well with them. It is therefore advisable to check the handiness of the individual models in the shop. The better the feel in the hand, the better the pliers work.
However, you must also be aware that each pair of pliers is designed for a specific cross-section of the ladder.
This means that not every pair of pliers can strip every cable. If a cable is too thick for your wire stripper, you may well damage the wires.