Now, unlike Telltale's poll, I'm going to list the big ones Paradox has published, not just what came out of actual Paradox Studios. However, I will pull anything that was published by Obsidian out of this poll, since they're gonna have their own poll (I figure they have enough of an identifiable style to have their own and they also have a history that stretches back before Paradox, so no PoE or Tyranny today).
Personally, my favorite (by far) is on Mount and Blade: Warband. A game it took me three or four tries to get into, but once I was hooked I was sinking hundreds of hours into it (I think I have well over a thousand). GalCiv2 would come in second, with Stellaris in third.