Generally you are better off to book with a TA instead of directly with the cruiseline. Booking directly with the cruiseline isn't any cheaper than a TA can get you. If your cruise price comes down, the cruiseline won't advise you of it but a good TA will constantly check if the price comes down. I check every couple of days on prices for booked clients and adjust their price if it drops. Not all TA's do this but a good one will. The only time prices can't be adjusted is after final payment(sometimes you can get around this) and if the cruiseline states it's for new bookings only. A TA can sometimes get you upgrades (if available) amenites and shipboard credits depending on the sailing. Also many TA's have group space blocked on certain sailings and can book you into a group rate even though you are not technically a group.
Have a great time on whichever cruise you choose!
Alicia
The world is a book, and those that do not travel, read only a page.
St. Augustine