Up to you. What you value? You should know the encyclopedia - on short term, there seems to be two Fire events, two Dark events, two Thunder events, and one of each of the rest.

Do you want to just spend one week before each event working on the counter element to that? Or will you prioritize some events more than others? Like maybe you'll prioritize single-player Advents since nobody can help you if you fail? Maybe you'll focus on the Wind raid to get more MvPs? Or perhaps focus on perfecting your Grid for one of the Union events?

There is no real answer, I'd think. It's all up to what you prefer.