I wish this decision was more easily defined. I honestly think Cass would make the best Divine, since Leliana apparently just goes murdering a bunch of people until they say "okay, I'll believe whatever you want me to" and Viv is too much a politician and flashy court lady for my tastes, while keeping pretty much everything the same.
However, apparently I picked all the decisions to get Leliana elected. I was playing as a mage, so I wasn't going to conscript the mages, even though they did really drop the ball. I'd rather work to reform allies and steer them in the right direction than force them into indentured servitude, pissing them off like the Templars did and getting a knife in the back later. If DA2 has taught us anything, it is that a mage will kill a person, then whine about it when they get thrown in jail and use that to justify them killing more people. And keeping the Wardens around makes more sense IMO than exiling them. They are still needed to kill Archdemons, and at the time the Inquisition still believed that Cory's dragon was an Archdemon. So exiling the only forces that can kill an Archdemon is stupid. Also, although the Wardens were incredibly stupid and did blood magic rituals, it was only after they had been manipulated into a perceived do-or-die situation by Cory's influence on the taint. So it wasn't completely their fault, even though they really went off the deep end with it.
As many have said, the Inquisition becomes the most powerful force in Thedas, it would be nice if the Inquisitor was given a more straight-forward way of supporting candidacy for the next Divine besides story choices. Maybe a few War Table missions, or a Chantry Revered Mother coming and asking the Inquisitor for their choice.