Beings of Tash Kalar
Both Imperial decks are identical. If you want to know more about the reasons, please read the History of the Decks. Both historically and thematically, these decks originate from the oldest form of the game.
As for features, the Imperial deck is relatively balanced with no big weakness. Its strongest feature is movement – many cards allow you to move other pieces, with either standard moves or combat moves (and a few other special moves). It is also relatively good at upgrading and destruction (with combat moves and with the gunpowder-based cards). It also offers several ways to slay legends.
The ability to move or upgrade pieces allows for intuitive gameplay. It gives you wide tactical range without planning too much ahead: Just summon a being wherever suitable; you may upgrade it or move it into position later. This, together with the fact there are two identical decks, makes Empire a good choice for your first games, but it stays interesting even much later.