What you're seeing here are very standard cruise booking options. You can either choose a particular stateroom (for a price premium) or book a "guarantee" stateroom which saves a few bucks but lets the cruise line put you in any stateroom in that category or higher. Some people place a lot of stock in that "or higher" phraseology, thinking guarantee staterooms are the best way to get complimentary upgrades. But the rule of thumb seems to be to book a category of stateroom you'd be happy sailing in; if no upgrade materializes and you're going to be upset, then just pay up for that next higher category in advance.