I suspect a lot of these agencies charge similar prices, but there might be other things to look at besides price, as a tiebreaker.

I recently got some online quotes via Cruisecompete (www.cruisecompete.com). One thing I noticed is that for the trip cancellation insurance policy I looked at (don't recall offhand which agency's it was), pre-existing conditions were excluded, and the available waiver of the pre-existing conditions exclusion only applied to people below 70. Well, I am below 70, but my mother is above 70, so I felt this insurance policy would be rather useless in our case.

I looked into Costco Travel (I'm already a Costco member), and the travel insurance policy was much better vis-a-vis the waiver of the pre-existing conditions exclusion -- no age limits are mentioned. Their pricing (for the cruise, taxes/fees, shipboard credit, insurance) was competitive, so the insurance thing was the tiebreaker -- I booked through them.

Just food for thought.