No, because they all have weaknesses.
Mewtwo: Chansey owns this set. The 'best' set for it in rby was the Grep set(Substitute~Recover~Psychic~Submission/ect), as there was no way to psuedo haze Sub. In anycase, even with the Grep set, all it takes is an Electrode to paralyze it, or an Exeggutor to Leech Seed it.
Tauros: Not the best because all it takes is a Thunderwave, and then it's about 100% that the OHKO's will be ineffective.
It was the best though and still is for making dents fast toward the end of a match when opposing Pkmn were worn down.