It seems to me that the playstyles of several advanced classes are very different to the playstyle of the basic, level 1-10 classes. The Assassin is quite different from the basic Inquisitor, for example, and the Scoundrel, with its stealth mechanic and Upper Hand resource, plays nothing like the Smuggler. Asking people to choose their advanced class based on ten levels of their basic class is kind of unfair when some of the advanced classes change your game experience so radically. What if, starting at level 10, you are able to choose an advanced class, but also switch to the other one by visiting your advanced class trainer. Then, at level 15 (about the time you should be finishing Dromund Kaas or Coruscant) you pay one last visit to the trainer to finalize your choice. This would let people dip their toes in both advance classes and see which playstyle they prefer, which still keeping the importance of the final choice.