How can this else if statment be improved?

I need to find out what is wrong with this code and how it can be improved. What if I were to get more values?

Would else if chain be better or a switch case?

string StatusMessage(int value)
{
  string message;

  if (value == 1)
  {
    message = "A";
  }

  else if (value == 2)
  {
    message = "A";
  }

  else if (value == 3)
  {
    message = "A";
  }

  else if (value == 10)
  {
    message = "B";
  }

  else if (value == 20)
  {
    message = "C";
  }

  else if (value == 100)
  {
    message = "D";
  }

  return message;
    }