Cancellation of April 18 Istanbul to FL

We just received fax from travel agent about cancellation of our cruise. Our choices are to switch to any other cruise of up to 21 night plus future cruise credit of $1,000 per person. or receive a full reund plus the same future cruise credit. Right now we are looking to replace this one with a cruise on the Navigator in the fall. We have only been on the Mariner and Voyager. Any recommendations?

Diamond 10/99
Song of Flower 02/00
Mariner 03/01 Maiden Voyage
Mariner 09/04
Mariner 11/05
Mariner 07/07
Voyager 04/08
Mariner 10/08
Navigator 11/09
Mariner 12/09
Navigator 11/10
Navigator 10/11
Mariner 1/12
Navigator 4/13
Voyager 12/14