The B starts off as your money and stays your money - you will always get the full amount upon your departure.
That may sound like a plus but in fact it is hostage money, subject to outrageous fees and offered only in deadbeat funds. Additionally, if your future plans involve living anywhere the economy is not directly related to USD/AUD/GBP or Euro you have no opportunity to save prudently - your retirement plans are totally exposed to currency risk. If that describes you, the A,B, and C are all the same: you may collectively call them the IMPROVIDENT fund.