Looks like Brawn would still be the team to beat - Renault's upgrade still doesn't seem to be able to match Brawn's or Redbull's. As it is unlikely it's going to rain in the desert
, Brawn should be strong.
If Redbull is able to manage to bring in new diffuser to Bahrain, than they could be tough to beat. The whole car is designed to improve air flow to the rear diffuser - so unlike some other teams who need to have major rework of their package, it seems to me they just need to fit a double decker on, to add more seconds to their car.
From some of Christian Horne's interviews... it seems to me they are quietly very confident with the new diffusers coming on.