What does the letter A1 and A2 mean on the cards?

Question

Memory cards

What is the magic letter A on the cards? Which is better, the absence of a letter, the letter A1 or A2? It seems like I found the info that A2 is better than A1, but I didn’t find it better when there are no letters at all. Who knows? I'm talking about SanDisk Extreme Pro MicroSDXC UHS-I U3 A2 V30 64GB
I'm trying to get the fastest card because I'm tired of creating difficulties at inopportune moments.