or does it vary based on where your fingers are "coming from"
That's exactly it, although you also have to consider where you're going. I must say, I don't use either of those combinations, I use 2 1 4. Luckily the G chord is one of those chords that is fairly "independant". When you're playing A maj or min you might want to experiment with 1 2 3 or 2 3 4 depending on the chord before and after it.