Savor or saver (cf. lifesaver) both seem more plausible. Why is there an i before the -or ending?
According to the Oxford English Dictionary, the history of the word's form is as follows:
The English form has changed (including being savour for a time), but from the history you can see that the vast majority of forms have had i or e or even y to maintain the pronunciation. This is because the word comes from the Old French sauveour, so English spelling has maintained much of its root.