Some people hear a difference, but each orchestra interprets a cue differently. That's not to say one is better than other - it's merely a preference. LA musicians have performed amazing scores with Williams such as Tintin and Crystal Skull so there's no reason to think they won't deliver now. With Williams conducting, he'll be able to do as many re-takes and make it sound to his liking. And they are giving him many months to record the score, too. This is probably one of the main reasons why Williams isn't scoring Spielberg's latest flick.