I think that Robbie Farah is a great player and maybe will end up the best hooker around, but I certainly can't rate him the equal of Smith yet. It's all very well to say "Oh, but Farah would go great if he played for Australia or in Origin!", but the fact is that he hasn't done either of those things and Cameron Smith has performed admirably at both. Equally Farah hasn't been in a position where he's been captaining a team and regularly acting as the onfield leader in the same way that Smith has.
At the end of the day both players have done very well over the last few years of NRL football. But only Smith has also proved himself to be a top class player at a higher level too. Until Farah does the same (and I agree he should have played Origin already) I can't rate him on the same level.