I've been with the DW series since DW2, and I would start with 7 or 8 (both are great, 7 is probably cheaper now) and avoid anything to do with 6. They actually cut out some characters with 6 without adding any new ones, and there were many cloned/shared movesets between characters (i.e. 5 characters would wield the same spear) which bothered people.
I would also argue that 6: Empires is the worst of all of the Empires entries that I've played because of all the features they streamlined and simplified even more from 5: Empires and moreover; it is an expansion to 6 which has the shitty renbu system for combat. But it is pretty cheap, if you want to try it go ahead but it might put you off the entire series.
