I'm going to say the EMS (at full potential) is flat-out the best. Its raw power (Perfect Susano'o) is comparable to Naruto's beast mode, and likely superior to all others, and it can also control tailed beasts, plus you gain a few powerful techniques such as Amaterasu, Tsukuyomi, Kamui, Kotoamatsukami, etc. depending on the eyes fused.