I haven't read all the other responses, but I have many ways to play A and it depends on the tune and context (what notes I need to ring).
If you need just the basic sound of A, laying the ring in the open position is fine. If you need the high E string to ring out, the best way for that shape in open position is 3,4,5th fingers. Reason being they're more narrow thanks to the pinky and can fit in the space easier. If you need the ring or pinky free for embellishments, then alter it as needed.
My favorite place to play it is probably an F shape moved up to the 5th fret. This allows for a lot of nice embellishments and a more natural fingering pattern. It's also very nice with the D shape on the top 3 strings or D string --11th, G string-9th, B string-10th with A and high E open (great shape).
There are many other great shapes so play around and find them.
Good job cleaning up your playing. I dedicated to that 2 years ago and it made a world of difference.