I prefer DW7 Empires. The Empires series has more customization, more freedom, character creation, and you can pretty much take over the country the way you want. the gameplay and systems overall feel more rewarding
and your actions have more impact than some scripted story.
DW8 Empires could be interesting though with the refinements and character and weapon additions.
The improvements to 8 are fairly nice. Though with the speed that they cranked 8 out at, I'd just wait for ~4 months and we'll probably hear word about 8:Empires.