Whatever works I guess ? Nooooooo
Folks if you're learning the A chord you are just starting out, so please please please don't go looking for shortcuts and an easier route to the one Justin prescribes. He has been teaching for decades and has refined many things to one make things easier and two to give you flexibility down the line.
Playing the A chord with 213 not only gives an anchor for changes to E and D but also keeps your pinkie free for playing suspended chords which are so very common in many many songs, those embellishments you hear over what sounds like the same chord.
Playing the A chord with 234 will stop you ever playing an Asus4 and playing 123 will make that Asus4 extremely awkward.
So take your time to learn what is being taught and work at it until you get it right. It takes time effort and concentration and some pain but getting it right at the start is worth it.
And peeps I am only saying this to help you, after spending 17 years looking for shortcuts and quick wins and getting nowhere fast and actually hampering my playing. Justin's methods work but you have to work at them for that to happen. Simples.
This is not a sprint, its a long old haul that never stops. Buckle down for some hard graft.
Cheers
Toby