Which are better, wooden or plastic cutting boards?

Well, technically, you should always use a wooden chopping board since they don't dull your knives like the plastic ones do. If you notice on the Food Network, they always use wooden unless cutting meat. Personally, I use the plastic ones since I don't have any decent knives anyway. Once I get some good knives, I will invest in a good wooden board though. And, it's easy to sanitize wooden boards. You just rub them with some lemon juice and salt. You shouldn't cut raw meat on them anyhow, so they are not hard to clean. Just a little soap and water.
Hope this helps!

Depending on the job, either material is a good choice.  Wood is porous and allows bacteria to retreat into the grain where it is trapped and dies.  With plastic, there is more of a chance of getting bacterial contamination from a non-porous, plastic cutting board.  Of course, this pro-argument for wood is rendered moot with a good cleaning and sanitizing of the plastic cutting board.

My personal preference is the Wood Cutting Board, and that's more for style than anything else, as it matches other items in my kitchen.