2009 = Maeda Atsuko
2010 = Oshima Yuko
2011 = Maeda Atsuko
2012 = Maeda Atsuko pulled out due to her graduation, Oshima Yuko won by a landslide.
Shinoda Mariko was centre last year for the janken senbatsu single 'Ue Kara Mariko', though! I think she'd make a great centre, but in the long term for Team A, they'll need someone like Rabutan or Wasamin to take over. I can tell they're pushing Mayuyu for AKB48 centre in general, though.