(Native) speakers read as /'spi:kəz/? Or /'spi:kəs/?

[NewHopeR]

Which one is correct? It seems both pronunciations are appreciated by many people?

[abaka]

Context, always context. A following vowel or voiced consonant tends to voice the [s], "speakerz-ov-English", an unvoiced consonant devoices it, "speakerss-seem-many". There are likely regional differences as well, but again, always depending on the surrounding context.