using If-else statements inside switch-case or vice versa,Which one is the elegant approach?

Note following code snippet:

Assume there are only two conditions take in to account and many number of cases

First approach

switch(x)
{
  case 1 : if(conditional1) { ... CODE BLOCK 1 ...}; else if(conditional2) {... CODE BLOCK 2 ...}; else {... CODE BLOCK 3 ...}; break; // nested if-else goes here

  case 2 : if(conditional1) {/.../}; else if(conditional2) {/.../}; else {/.../}; break;

case X: /... similar pattern follows until default .../ break;

default:break;
};

and Second Approach other-way around

 if(conditional1)
    {
     switch(x)
        {
          case 1 : /... CODE BLOCK 1 .../ break; 

          case 2 : /.../ break;

        case X: /... similar pattern follows until default .../ break;

        default:break;
        };
    }
    else if(conditional2)
    {
       switch(x)
        {
          case 1 : /... ... CODE BLOCK 2 .../ break; 

          case 2 : /.../ break;

        case X: /... similar pattern follows until default .../ break;

        default:break;
        };
    }
   else
    {
       switch(x)
        {
          case 1 : /... ... CODE BLOCK 3 .../ break; 

          case 2 : /.../ break;

        case X: /... similar pattern follows until default .../ break;

        default:break;
        };
    }

• Hope you understand the code pattern

Which approach helps C/C++ compiler to generate better optimized code(obj size and control nodes) ?

If N = Number of Conditional statements , If M = Number of cases ,

If we take N and M parameters in to account,how can we determine which approach is elegant?