In the US I usually find the best cruise rate best as soon as published .
Cuinard always has a Sale going on , mostly adding OBC or upgrades .
Should I find something better before Final ,I can cancel , rebook and move my deposit .
I always use a TA as they are permitted to discount Cunard rates and Groups which may add OBC , and other amenities.
I always compare booking Direct and via my TA . TA always wins out as the best deal 100% of the time.