I don't like small decks. But the developers say that small decks are better. Has anyone some experience with big decks? I don't need the full 30. But 20 seems so small.
I have a small dck but I'm too embarrassed to use it
Yes, small decks are most of the time better. There are a few exceptions like Stromberg or Lightsworns where you don't want to deck out too quickly and thus want to have more than 20 cards. But usually you want to keep the amount of cards in your deck as low as possible to increase the chance of having a good starting hand.
Less cards = better consistence. You'll need a lot of searchers to make a bigger deck work.