I use 20 cards because it's easier to get through your deck and get the cards you actually need into your hand and onto the field.
It's usually not advised to have more than 24 cards at max unless you have a deck that is specifically made to do so, other than that it will actually be able to decrease your chances of winning by quite a lot.


Also I just got a mirror wall card from packs and currently leveling up my Bakura so I can test out some of his skills.