Based on what we've seen from all 3 guys so far this preseason and EJ's past 2 minute drill performances, assuming nothing significantly different happens in the next 2 weeks, I'm really hoping they keep all 3 w/ Taylor the starter, Cassel the backup, & Manuel #3.
Taylor seems to have the highest baseline (not floor) of the 3, and Cassel should be serviceable in-game if Taylor is injured. If they get to the 4th and need to mount a comeback, EJ seems to play best when he doesn't have time to overthink things and he has the strongest arm of the 3, so it seems he'd give a solid shot at the comeback.
I'd agree w/ the OP that in that final drive EJ looked like he'd've been good against the 1's.