13 is better i think, there are some bugs in 11, 13 has most of them resolved, i would go for 13 for better gas mileage, less wind noise. i will be getting one in two months.
2014 328 GT Msport, Mineral Grey, Premium Package, Tech. Package, CWP, DAP, Lighting Package, HUD, Harmon Kardon.
2013 328xi Mineral Gray, Moonroof, CWP