Because it's the style I use, and because I don't need to bug-check the indented code to make sure it's braced correctly, I find this easiest to read:

  while ((len = getline(line, MAXLINE)) > 0) {
      if (len > max) {
          max = len;
          copy(longest, line);
      }
  }
  if (max > 0) { /* there was a line */
      printf("%s", longest);
  }