I don't get why emancipation and confessions are considered so good. Confessions specially is one of Madonna's worst albums. As for TEOM I will just say that charmbracelet and E=MC2 are superior. I guess chart success does affect critical reception for some.
For the 90's Madonna. She pushed barriers and experimented more. I like 90's Madonna even more than the 80's one. For the 00's I definitely choose Mariah.
Overall? Mariah. Why? Because She is so much better of a singer and has a more consistent material than the material girl.
P.S. Whoever claims that Mariah has an irritating voice must be joking... I mean really? You have to choose between Mariah and Madonna and you choose based on voice Madonna? I will just remember one incident going to my aunt's house as a family in the late 80's and Madonna was on the radio. As she was talking with my parents suddenly she paused and said "Jesus. Is this cat a recording artist? She is "meowing" instead of singing."