I want to add some specific definitions since d&t are new cruisers.
Oceanview/Outside Gauranteed Category:
You are gauranteed an Oceanview Cabin on any deck and anywhere they want to put you. This option is very often upgraded to a higher deck with an identical cabin. This will be a TBA "to be assigned" You can call and get your Cabin assignment usually 7-10 days before the cruise.
Best Fare Cabin Assigned:
This option is the same price but you actually pick your cabin location and number. And is usually not upgraded.
I would get an Oceanview cabin for your first cruise, or even a Balcony if is in the budget.
After a few cruises you may find you don't spend that much time in there and would rather cruise more often with an inside cabin as is my case, and spend the difference shopping and exploring!
Best to you again,