I'm kind of a beginner as well but I always thought the longer the blades the slower the headspeed which translates to smoother hovering and forward flight (more lift). The shorter the blades the faster the headspeed and the more responsive the bird will be in 3D.

For the beginner you'll want the longer blades, it's much more stable. Check out Tech Model Products, I've been using the 335s and they are pretty decent woodies:

[link=http://www.techmodelproducts.com/trex_450_parts.php]http://www.techmodelproducts.com/trex_450_parts.php[/link]