There are couple of things to consider when booking your cruise.
If you book through Disney directly you will be in control of the reservation. You will be able to make changes to the ressie with no problem. But you will also be responsible for looking for and finding new promotions. You will then have to call
DCL and get them to apply any promotions to your reservation.
If you use a
travel agent, any changes made to the reservation will need to be handled by the agent. DCL will not let you change the ressie. (You will still be able to go online and book on board activities on your own). But some
travel agency do offer a service of watching your ressie for future discounts and will have them applied to your ressie if one is available. Also many TAs will offer you gifts or on-board credits for booking through them
The prices of the cruises are pretty much standard across all TAs. Look for a TA that fits your needs. Some TA work out of the traditional office. Some work exclusively online. Other based on phone calls. Also look at any incentives the TA is offering.
We have used
Dreams Unlimited Travel as our TA since they were incorporated about 10 years ago. We have been very pleased. They do business exclusively online - no office.
I am sure others will chime in with thier experiences with other TAs.