The Star Flyer will be more romantic, and is more likely to visit some of the smaller islands. On the other hand, night life will be more party-like on Costa. Depends on what you prefer, as to whether you'll be bored.
I was asking regarding my two kids. My husband I will love it> I think they might be bored out of their minds. Maybe I should book the Costa for all of us. I'm just so tired of the bigh cruise ship. Thanks for your reply