You get rewards based on your highest rank between all modes. If you have Legend in Classic, Standard, and Wild, then it'll go with the highest of the 3.
Example: Legend 263 Classic, Legend 105 Standard, Legend 357 Wild, you'd get rewards for your Standard rank since it's the highest.
if i get legend both standard and wild do i get more rewards at the end of the month?
No, not really, you'd get rewards based on the highest rank you achieved regardless of the mode
You get rewards based on your highest rank between all modes. If you have Legend in Classic, Standard, and Wild, then it'll go with the highest of the 3.
Example: Legend 263 Classic, Legend 105 Standard, Legend 357 Wild, you'd get rewards for your Standard rank since it's the highest.
The rewards for legend are the same, irrespective of the rank though...