I vote for all three.

    * Types so I can prevent all the low hanging fruit.
    
    * Contracts so I can encode invariants that the types 
      can't always express.

    * Conventions so that everyone is talking the same 
      language and there is less confusion

My goal wasn't so much to promote any specific answer, just to rebute the argument that the solution to memory safety bugs is to have better C programmers

Types because they can be checked mechanically, simply enough that a programmer can understand the checking process and why it fails or succeeds, but are expressive enough (given some relatively cautious/widespread advances - HKT and some level of dependent typing) for every invariant I've ever needed.