I've toured with a trailer, and I've toured with panniers. For a fully loaded tour I prefer the trailer, but for a tour where I'm staying inside instead of camping (assuming that I am starting and ending in the same location) I'll choose panniers. I have an article up on crazyguyonabike.com that summarizes the good and bad of both. If you're interested, here's the link to my article: Panniers, a trailer, both?.

Happy touring!