Tevinter has slavery(and this slavers running around Thedas), blood magic,blood sacrifice, an ancient history of invading foreign soil, and to top it off out of control mages running the show.
On the other hand Orlais has masked slavery(both in the form of 'servants' and feudal peasants), an unhealthy amount of rape directed at the general populace, a modern history of invading foreign soil, a corrupt chantry in their pocket(and thus the whole oppression of mages thing on their shoulders), and to top it off corrupt and out of control nobles running the show.
I'd say they're both pretty awful, but the biggest douche award goes to Orlais since you know they're still super powerful and throwing their weight around. That's just my .02 cents.