fgets is faster but stream_get_line is more useful in a tcp server scripts.
when fgets reads some bytes from socket, where EOF is reached, it returns bool(false) same as stream_get_line
BUT if remote client drops connection, and server script will try to read some data with function fgets, function will return bool(false), and stream_get_line will return string(0) ""
so you can detect remote client disconnection with stream_get_line, and cannot with fgets