Which Splinter to choose to rise up on ladder / Leagues

I just recently entered the game and realized that some splinters are far more consitent than others (at least at lower Leagues).

While I really loved Death, I just recently started to use Life a lot more and getting through my battles way better.
However, after a while I started loosing a lot against water.....

Do you have any advice on strategy / meta for the Leagues? I can't afford to level up all splinters the same, so I have to choose 1 or 2 to focus on.

Thanks a million!