What kind of fighting are you talking about? I thought I had seen dog fights until this past season while I was pheasant hunting. One shorthair turned on the other and they laid into each other. Holes in ears, jowels, legs. It was nasty! If this is not the kind of problem you are experiencing, definitely let them duke it out, and establish the pecking order the other guys have mentioned.
Also if it turns into a locked up dog fight where they are actually tearing eachother up, don't grab them by the collar to pull them apart. (Good way to get bitten yourself) You need two people to do this, but go up behind the dogs and grab their back legs out from under them and just pull the dogs away from each other. This makes the dogs feel like they have lost control and they will turn loose then. Good Luck.