For competitive shooting, depending on the discipline, there is usually a minimum to max trigger weight. 5.5 lbs is the lowest weight allowed in service rifle competition for example and these guys shoot prone, kneeling, sitting and standing in some cases, out to 800m. The average AR factory trigger will work but a nicely polished one, not a replacement one, is all that is allowed in some cases.
Although some people have the belief that lighter is better, I have always felt that "Crisp", that is it breaks like a glass rod, is better. A light but mushy trigger will do you no good where a moderate to heavy but crisp trigger will do you much better.
There are some very simple modifications that can be done to the existing trigger set up to lesson the perceived trigger pull, the amount of take up before release, usually called "Creep" can be removed by simply running a 1/4 by 28 set screw into the pistol grip screw hole, #### the hammer, out the safety on and run the set screw in until it stops. Then turn about 1/2 out so the safety can operate freely. As you tighten the screw you can watch the back end of the trigger rise up in the receiver and remove some of the creep.
There are other things that need to be done to make it better but I'd rather not explain those as doing them improperly will cause the trigger to malfunction.
Scott