Pegasus is that it won't add duplicate addresses to a list. So the duplicate additions aren't a large problem. Once in a while I've gotten a few duplicates. But that's okay.
Aureate blocks duplicate addresses on import as well.
In Pegasus, additions are added at the bottom, no special order. In Aureate, after import, I sort the list by email address, alphabetically. Then it gets tossed back into Pegasus. When bounces or problems come up after each mailing, I can open the list in TextPad OR Pegasus and just go down alphabetically to delete addresses. It's less than a dozen or so mouseclicks to import and sort and export back to Pegasus.