I say Minn-oh-tore. Which I'm pretty sure is wrong.
Um, doesn't it come from Greek? Specifically, Minos the king of Crete?
I've always said, and usually hear, sen-tar.I've always pronounced it "mino-tor", just as I say a centaur is "sen-tor".
The spelling comes from the Latin. Most greek names were transliterated by the Romans... and those are still used.