Probably the 360 will sell better through summer than the PS3.
September will be a good month for Sony but maybe we´ll see a fight between all 3 companies - Metroid won´t be released before June but September is 2 months later and it´s time for Brawl and Mario Galaxy too. And honestly Metroid and Mario (I expect to see at least one title in September and another of the "big 3" till December) will sell better than their GC counterparts. Probably it´s still the same order (Wii > 360 > PS3) but all systems will sell better than they do now.