In that period Fed played most of the time just slice BH, even on clay. Try to imagine a modern game player who is playing most of the time just slice on one side and is ranked in top 10, pretty unimaginable. Fed, by playing slice BH had the best 4 consecutive years in open era history, that's how his forehand was good. Take Tsonga's or Delpo's bashing FH on the day when everything is going in and you'll get Fed's FH in 4 years time with exception that watching Tsonga or Delpo you get an impression that those are risky home run shots with big margin for error, watching Fed hitting those FHs you had a feeling like he is taking some zero margin for error basic shots
I agree with all these, except the all slice period, which is not true.
But as a Fed fan you can hardly find many ppl appreciating his game more than i do, yet i try to be objective and Rafa's FH is a shot that had me impressed since the very first few times i watched him. No one else can create this rotation, with the necessary speed and a real minimum margin for error, all the banana passing shots, etc.
It's probably a narrow margin here and possibly a matter of taste, or personal opinion, coz they're both incredible shots indeed.