Not knowing the itineraries of the various cruises I will not comment specifically on any of them, but I suggest that whichever one you eventually choose, make sure you do one that includes the overnight in Reykjavik. This gives you the opportunity to take in much of what there is to offer in the area and without the pressure of having to return to the ship in time for sailing you can arrange your own tour with a local company in smaller groups and cheaper than the cruise line offerings.