Mallorca vs. Sardinia vs. Porto

Hi! My fiancée and I are trying to plan a honeymoon for around a week and a half in mid-September this year. We're looking for someplace in Europe to do a mix of relaxing and exploring. Heavier on the relaxation side, but exploring when we get restless. We've narrowed our search down to Mallorca, Sardinia and Porto. We've been to Porto before and loved it, the other two would be new to us. I'd love to know if anyone feels strongly about any of these locations over another. Thank you!!