As much as Satoshi getting Mewtwo would have been the historic moment in series, I still kind of think that the only character "worthy" of having him really should be Sakaki (or Giovanni, if you will).
I can't quite explain it why, especially since Mewtwo is on good terms with Satoshi, and probably hates Sakaki the most, but at the same time there is just something powerful in Sakaki's general personality, that it makes him fitting to be Mewtwo's trainer.
I also even had some ideas about Mewtwo being the key factor in Sakaki changing his ways, but it will never happen anyway.
I can't quite explain it why, especially since Mewtwo is on good terms with Satoshi, and probably hates Sakaki the most, but at the same time there is just something powerful in Sakaki's general personality, that it makes him fitting to be Mewtwo's trainer.
I also even had some ideas about Mewtwo being the key factor in Sakaki changing his ways, but it will never happen anyway.