I think it would depend on the opponent and the defensive tactic you're playing.
if you play full court press or 1-3-1 then you might put it on PG to get more steals, but then again if the opponents best scorer is a SG you should put him there, and if you play 2-3 there's no point on putting it on SF.
So, study your opponents strengths and knowing your weaknesses try to compensate by switching defenders differently in different games.