But they know that we aren't. Mark my words, either they will refrain from announcing a prime ministerial candidate, or more likely they will field some very respected technocrat or business leader. They simply cannot afford to make it NaMo v/s RG, because then a potential defeat would be converted into a potential bloodbath.
There were rumors recenty that Nandan Nilekani might be their choice. They will make a move like that to put a modicum of competition to Modi's image, rather than put up a greenhorn like RG. Even people who are not Modi fans will feel compelled to vote for the BJP, if they see RG as the congress candidate for PM, because he has not even held an important ministerial post at central or state level to date.
Remember how Sonia played a political masterstroke in 2004, by making MMS the PM even though she had the mandate? That gambit easily won them allies, who may not have been too keen on an alliance with SG at the helm. Similarly they will find a figurehead respected by everyone, instead of RG whom only fawning congressis pretend to respect so that they don't lose their jobs.