ok, this might surprise all of you but the cruise line has nothing to do with taxes and port charges. They are determined by the gorvernment. Two cruise lines can have almost identical itineraries and the charges will be diffferent even if one port or the embarkation port is different. The port charges are set by the port authority as I mentioned. That is one reason cruising the Panama canal and Alaska can be high, the port charges and taxes are both out of the ordinary.
Now, as for the tips and gratuities, please don't even get me started.