Fire, Darkness, Life.
Fire has the raw power and devastating destructive force for creatures and permanents. It is very vulnerable, but when your main export is offense, there isn't a huge demand for defense. But luckily, the small defense it has can be devastating to many opponents. But mostly it's ability to shut down your damage via destruction while giving it's own output of damage makes it number one in my book.
Darkness has power and strong flexibility. It can keep itself alive while playing on the opponent's strength. Stealing their permanents grants them an advantage while giving your opponent a disadvantage. Not only does it have the power to shut down the opponent, it can do so in many ways, making it very flexible. Paired with strong attackers, and a good defense, it's a very balanced and strong element.
Life I feel is a strong element, but not in the sense of power. It has fast, consistent damage, and can fully support itself, keeping itself alive until you just cannot go on any longer. With the latest additions, it can poison and creature spam like no tomorrow. It rivals fractal, maybe not on speed but on the principle of power.