There seem to be about as many answers to this as there are members here; everybody has their favorite way to book. About the only thing everybody agrees on is that cruise prices change--frequently.
My advice to you would be, since this will only be your second cruise, stick with your travel agent since you seem pleased with them. You might save a few bucks doing it yourself, but until you have a few more cruises under your belt, you could also really trip yourself up--costing you more in the long run.
When you are a little more seasoned you can try it yourself; but there is a lot to be said for having a relationship with an agent that knows your likes and dislikes. And they can sometimes get perks for you that you couldn't get yourself.
Good luck and happy cruising!