I'll try and answer your questions one at a time:
1) The main difference is essentially the UI and the way files are uploaded. The Customer Attributes interface is essentially a skin over the AAM instance on the backend. As you stated, the Customer Attributes interface is basically drag & drop. AAM requires you to upload your data directly to the FTP server. The format of the data being uploaded needs to be the same as it ends up in the same system.
2) There isn't really a recommended approach on when to use each method. The AAM interface is obviously only available to customers with the AAM solution as part of their contract. The Customer Attributes interface is available to all Marketing Cloud customers. The AAM interface is a bit more advanced with more options for how the data is processed where the Customer Attributes is simple.
3) No, AAM doesn't have the same interface. The advantage to using the AAM interface is that it provides more information and greater control, but if you prefer the Customer Attributes UI, you should continue to use it.
1) You can view the first ten rows when you view/edit schema in Customer Attributes. In AAM you have more options for what is visible.
2) We don't really have a rollback mechanism, but depending on how the file is being written that may not be an issue. From an AAM point of view, if the file is valid, we will process it. Usually, however, if there is a problem with the FTP upload, it will register as a partial file and our system will reject it
Thanks Jantzen! Your clarified all questions, I'll get back to you with more doubts in other AAM functional areas. Thanks again!
Glad I was able to help!