I thought I would bring back the endless debate of what takes more skill: realism or stock.

From personal experience I have to say realism. Simply because after playing realism for a while I just own everyone in stock.

It seems that realism forced me to start shooting everyone in the head (since that is sometimes the only body part you see in realism). So switching to stock I have no problem with any enemy, even the shotgun whores everyone complains about.