Italy, Greece, or Portugal… help!

My fiancé and I are hoping to go on our honeymoon in October. I have never been to Europe before and we have decided we should try to do one country since we will likely only do 10 days there. Although he has been to Italy before we both agree it should be considered- is there anyone who has been to all 3 places who has an opinion of which would be best for a honey moon with a little adventure and a little relaxation?

Thanks!