Clearly, Brady is the choice if healthy. Bledsoe has been healthy for a while now, and Belichick stuck with Brady because he was winning so much. Why change now? Brady has continued to play pretty well in the playoffs. Yes, I think Bledsoe is probably more talented but he is rusty and Brady obviously brings something to the table that Bledsoe does not.
I have heard some analysts say "well, Bledsoe can throw the ball downfield better so he will fare better in a shootout". First off, I think the Patriots probably want to at least try to avoid a shootout (doubtful, though). Secondly, throwing the ball downfield isn't a quarterback's only job. Jeff George can throw the ball downfield pretty well, would you start him over Brady just because you were going against the Rams? Uh, no.
I think Bledsoe is a great QB but Brady has earned the right to be under center on Super Bowl Sunday.