Students have been asking me whether wood or plastic boards are better for as long as I have been teaching. The answer is: what matters more than the material is the way you take care of your board.
Plastic boards are non-porous, which means they are easier to clean than wood, which is porous. But as long as you wash them with hot soapy water, rinse with clean water and dry, both are good. You can also sanitize boards with an unscented bleach solution of 1 tablespoon per every gallon of water. Let the mixture sit on the board for a few minutes, then rinse.
I use both plastic and wood in my kitchen. I prefer the feel of working on a wood board, and use that for everything but meat and poultry. I put my plastic boards in the dishwasher, which washes them for longer and at a higher temperature than I would at the sink.
Whether wood or plastic, if your board gets deep cuts and grooves, it should be replaced, as those areas can harbor bacteria. For more information about what you need in the kitchen, see Must-Have Kitchen Essentials.