Not the best or the most flexible ones, just the ones I enjoyed the most. Usually ones with weird interactions or ones that do something special in that specific deck. Basically just stuff I tried out.
One thing people don’t always think about is that even though may not want to break down your carefully crafted deck, you do actually play more games with sideboard available than not in tournaments. This seems to be a problem especially among newer players, who don’t often have any sideboard whatsoever.