The first deck that I actually did well with was a Magmortar / Heatran deck. It was probably my favorite deck I’ve ever used because it was fun to play and if I could get setup then I could just crush my opponent. I stopped using it because it was too slow and couldn’t keep up with the new cards that were coming out. Unfortunately that is the way things are now. A certain deck will be really good and winning tournaments left and right but then another set of cards will come out and then that deck will be almost unusable.
I like to use many different decks and use a different one at almost every tournament I go to. This gives me an advantage sometimes because people will think that I will use this deck but I’ll use another. If you switch out decks after every tournament then you will probably do better but then again you might not. It all depends if your opponent has a deck that is good against yours or not or it might be an even matchup. Basically it all depends on luck.