Truthfully I have been in the camp of 'the best QB for the team' and while I have never been a fan of Cassel since his days with the Pats* I have been one to support EJ but even I can see he has virtually zero shot to win this starting QB job.
EJ just makes some maddening throws at times, and then he makes throws that few QB's can make. But despite this, his 58.6% completion percentage is widely criticized (and I can understand that) but Matt Cassel has a 59% completion percentage. So what is the real difference there? To me starting Cassel would be a mistake because we pretty much know what we will get. Orton from USC. Could the Bills win 10 with Cassel? If you factor in our huge coaching upgrade and better OL play to be expected, sure I can see that happening. But the ceiling isn't as high IMO when you compare it to EJ and Taylor.
EJ and Tyrod Taylor both have inaccuracy issues, but where Taylor separates himself is his poise, leadership in the pocket, and his ability to make a more explosive play with his feet. Ad Taylor has been in the NFL longer, and learned from Flacco and a top organization. That to me is huge. He is ahead of the curve. Could EJ blossom later in his career? Maybe. With the right coaching and working on the shorter throws, he can be.
But for now to be its clear: Start Tyrod Taylor Week 1 against Indy.