Due to the untimely passing of Leonard Nimoy and Chikao Ohtsuka someone needs to steep in for both of them.

My choices- English: Hugh Laurie or Corey Burton

Japan- Akio Otsuka

The only reason I don't want Corey Burton is he already plays Ansem the Wise AND Yen Sid, seems like it might be a bit much.

My go to recommendation would be Frank Welker, who besides being generally great, voiced a character also voiced by Leonard Nimoy with Megatron/Galvatron in the original Transformers.

Don't have any opinion one way or another on the Japanese VA.

Someone who can do a good job of doing the voice that Nimoy/Ohtsuka used for that character.