I was taught form #1 and I played it that way until I dropped playing. Fast forward 35+ years when I picked up guitar again and I again made Gmaj as in #1. Then I noticed two things; something in my technique was causing my third finger to be too high above the fret and it sounded terrible and, one or more of the instructors on this and other sites were playing form #3. I tried it and my pinky natually fell where it was supposd to, i.e., just above the third fret, E string. The note was much more accurate.

I asked a friend about the two chord forms and he called #3 a "folk G." I asked if there was an advantage between the two and he thought having the index finger free (form #3) might make for easier/quicker fingering beyond just the chord itself. I decided to switch. That was in late October.

It took quite awhile to replicate the speed of the chord change I could do with form #1 but it has finally dropped into place. For *me*, #3 gives me a better sounding chord.