"Does class A guarantee that they is better quality?"
I believe it works like this*:
A: Alpha can be unstable and will cause crashes.
B: Beta is feature complete but likely to contain a number of known or unknown bugs. (C and D are incremental improvements of this)
E: Enterprise is the marketing stage at which all necessary commercialization activities have been completed and a product is available for purchase. Depending however, on Government or region.
F: Final version that is for release to all, comes with massive support costs compared to E above. (Usually occurs when the next generation hits level C.
*Not really, total snark. ☺