Concatenating strings in C, which method is more efficient?

I came across these two methods to concatenate strings:

Common part:

char* first= "First";
char* second = "Second";
char* both = malloc(strlen(first) + strlen(second) + 2);

Method 1:

strcpy(both, first);
strcat(both, " ");       // or space could have been part of one of the strings
strcat(both, second);

Method 2:

sprintf(both, "%s %s", first, second);

In both cases the content of both would be "First Second".

I would like to know which one is more efficient (I have to perform several concatenation operations), or if you know a better way to do it.