Both are fine, it is more a matter of personal preference/local usage. Some people use both. Same with "either"

Dear Daniel, In my experience with people here, some people from the New England area say either (i) and neither (i), while everyone else I've met in the north as well as in the south and the west, use neither (ee) and either (ee). Also, I have heard people from other English speaking countries use the (i) pronunciation. Saludos, Miranda

Either or eether are ok!