[Jeff22]

A lot of good observations in this discussion.

I shoot single action auto pistols and DA/SA auto pistols and double action revolvers and Glocks and a Sig DAK. I switch around pretty frequently (although the Sig DAK is currently my duty gun). I have big hands and long fingers. I find I have to switch around a little bit depending upon which gun I'm shooting.

The length of pull from the face of the trigger to the backstrap is critical when achieving a proper fit of the gun to the operator.

With DA revolvers I usually use the crease of the distal joint (What Mas Ayoob often calls "the power crease") and with anything else, I contact the trigger with the pad of the first joint.

Your instructor in basic training wasn't necessarily wrong -- contacting the face of the trigger with the pad of the first joint is usually the first choice with any rifle. (However, one of my friends has been shooting M16/AR15 platform rifles since he was in the Army in the 70s and he uses the "power crease" when running that system, BUT the pad of his finger when shooting any other rifle . . . )

You'll probably just have to experiment to see what works best for YOU on any particular weapons system.