Is it best to book a cruise on-line or thru a travel agent???

The best thing to do is just to search all of the cruise deal web sites, find a cruise that suits your dates and area that you want to cruise to and has ports that you like, find the best price then go to a travel agent and ask them if they can beat or match the price you have found.
If the best they can do is match the price, they will offer you some incentive like free insurance or on board credit, if they don't or can't better the offer, go somewhere else. The best deals need to be worked for.

Either ways works. If you want some service and more guidance go with the travel agent.

If you book through a local travel agent, you've got some leverage in the event you have a bad experience.

I've found that booking directly through the cruise line is the least expensive way to go.

online is the way to go. check out this site, it is an aggregator which means it takes prices from all the travel websites and gives you the best deal out there. good luck! http://www.ytbtravel.com/travelcuse