my DH has both, and it's an age thing, same basic machine with a lot of modifications between them. There are a lot of parts on the E that are quite different than the A, and a lot that are the same. They have about the same abilities, take the same cams, bobbins and cases. I know the thread guides are different, the tension is different, the back side housing is different. . . though my DH says inside they were about the same.
If you are getting a sewer - one is probably as good as the other - if you need a parts machine, they are not the best match.