[quote name='ctrek3']how does amazon digital downloads compare to steam?[/QUOTE]
Amazon gives you your game key in your Amazon account and the game installers, basically.
These game installers are the files you'd want to back-up somewhere [DVD's, BR's, another HDD, whatever] - if you want to avoid having to re-download them.
Amazon is decent enough, if you ask me.
You can re-DL your game installer files as much as you like on as many PC's as you tell it are yours.
Also, like many other new EA games, DAO - Ultimate activates up on Origin.
So, you could just take the key from Amazon, register it on Origin, and do the 27 GB download through Origin.
If you have trouble activating any of the DAO Ultimate's DLC,
see this post on Steam.