[2021] New player here, what is the difference between the berserkers combos?

You will get more and longer combos as you level. Everyone has different preferences. Just experiment with what you have and see which you like best for certain situations. Most zerk combos have stuns or knockbacks built in. It's mostly about maximizing your damage without leaving yourself too open to get hit yourself, so knowing your combos and when you can build in a timely dodge-roll is key