I subscribe to Cruise Travel and read Porthole in the bookstore. I had become disappointed with Cruise Travel as there hasn't been much substance and very little "critical" reporting. However, the last issue was wonderful. It is a good value and would recommend if only for the ship information and the letters.
Porthole has always seemed to be fluff and advertising. It is expensive; that is why I usually try to read it for free in the bookstore. They do have some great articles about port visits and usually have better researched articles than Cruise Travel. Still, I think Cruise Travel is a better value and more enjoyable reading.
Hope this helps.