Who gains, who loses ? impossible to predict. The new tires and the aero will be obviously decisive.
All I can say is that teams like Williams, RedBull, Mclaren and Ferrari have already done full scale aero tests on the Pirelli tires in Abu Dhabi. Renault and Mercedes did not... maybe not yet. They concentrated on the rear wing.

(last photo taken in Jerez 2010)
I also notice that every time the tires changed, one of the top teams made mistakes and 'lost ground'; Ferrari in 2005. Mclaren in 2006, Renault in 2007... With the mandatory weight distribution, maybe we wont see such thing happen again. But limitation on testing and homologated parts wont help the ones who will do mistakes...