DonovanB wrote
What Bob said about G highlights the many variations you can get from different fingering patterns. If you keep your index finger free it is easier to move to G7 as well.
It's also easier to get to C, Am, Em....
It's worth trying different fingerings for chords. Some of them will free up another finger that can be used to add colour EG having the index finger free when playing an open G chord, or having the pinky free when playing a D.
Some fingerings will also make changing to other chords easier. The free index finger on the G chord played with fingers 3,2 & 4 will make for quicker access to several other open chords.
The optimal fingering may depend on context, what you've got to move from and what you've to to move to, or what key you are playing in.
So experiment. If you are designing drills then design different fingerings into those drills.
And don't be afraid to use that thumb on the 6th string. Sometimes that can simplify things hugely - make it quicker to get a chord down or to shift to the next chord or to free up a finger.