Around here, right after Christmas break is when Webelos families start deciding which troop to join. Most cross-overs occur in February at Blue-Gold dinners with a few Packs crossing in March.
Before a Cub Scout family decides on a troop, they really should investigate all their options. After all, this will hopefully be a group they will be associated with for at least 7 years. Some towns have a single Boy Scout troop, while others have a handful to choose between.
I've got a set of questions and some prefered answers at Joining Questions that will help get your mind thinking in the right direction. Every troop has a different personality and each scout will want to join one or another for his own reasons. It's important that the family consider the values of each troop decide on which one will be a best fit for the individual scout's enjoyment, advancement, and accomplishment.

Scout On