From the reports that I have read, most blogs state that RBR looked better (as in, on rails), than the McLaren.
Also consider that RBR have a better design team and I feel that they are more likely to make progress during the season. Another points to consider is that during the break, RBR always come back nigh on unbeatable (this might be because they were work on their car during the break, where other teams take a real break...who knows).
In summary, with the limited evidence we have (predictions are heavily based on guess-work and gut-feeling), I believe RBR will have the best car in race No.1 and also averaged throughout the season.
Also consider that RBR have a better design team and I feel that they are more likely to make progress during the season. Another points to consider is that during the break, RBR always come back nigh on unbeatable (this might be because they were work on their car during the break, where other teams take a real break...who knows).
In summary, with the limited evidence we have (predictions are heavily based on guess-work and gut-feeling), I believe RBR will have the best car in race No.1 and also averaged throughout the season.