Fl Slayer beleive it or not can be tweaked to sound good, not all people do it correctly though. It has more of a 90s sound to it IMO.
However for the best possible guitar you'll need a real one.
You'll also need a good mic to record it.
Fl Slayer is a good start if you plan on writing a song but I wouldn't use it as your main plugin. I know of some good guitar VSTs but I think you'll be better off recording your own.