So, I'll try to describe my point of view. The first candidate is Vivenne... She is the most conservative one and she likes the original system which has given her power and status. She doesn't want even to try to understand the rebels because she has never faced their difficulties. Vivienne was lucky to seduce duke Bastien and to become a courtier with his help. She doesn't understand or doesn't want to understand that not every mage has such a chance. She is very selfish and hypocritical talking about how dangerous magic is and how loyal to the ordinary people of Thedas she is, but... Okay, we'll restore the Circle and what? Will you be so willing to return there? Why not?! Magic is dangerous like fire is dangerous! You're dangerous and you can easily become an abomination! So, no more dukes for you, no more court intrigues, no more freedom. Vivienne thinks that all mages should be kept in prisons and she also thinks that she deserves to rule over them. She herself would NEVER submit to anybody. But theese are the traits of her character and now let's talk about her being the Divine. In both variants (allying with the rebel mages or conscripting them) she brings down her fury upon the people who've saved Thedas from Corypheus. She doesn't give them any chance because she doesn't want any resistance, any threat to her power. She gives mages more freedom and responsability, but also creates a new Templar order to control them. Maybe some mages will be able to hold some political power now, but only these who support her and her course of action. She'll try to get even more power for herself brilliantly playing the Game and maniplating the monarchs and nobles as well as huge masses of her favourite ordinary people. She is clever and sly, she is a good politician and she'll be able to hold the position, but her own power is more important to her than all this "serving the Maker and the people of Thedas". And there also will be a lot of bloodshed if she is the Divine. A lot of revolts and fightings with the rebels. Do we need a new magocracy? I don't think so... And what will happen when she is dead? It will be very difficult for another mage to take her place and the new Divine will try to leash the mages giving the templars more power, turning them into a strong counterweight. The Chantry needs reforms and Vivienne can't provide them. No.
Cassandra is in the middle... I believe that she is the most popular candidate and she also leads the Chantry to its golden age. She does good work reforming the Chantry and dedicating the Seekers of Truth to the right purpose, but mages fight with each other now. Either the College rivals the Circle or there is a shadow war in the new Circle against the members of the Bright Hand who want to gain more freedom and the Inquisition's support. At least Cassandra doesn't try to return all mages to the Circle without their consent. And she thinks about people, not about herself like Vivienne, But the most important problem with Cassandra is that she really hates politics and can be easily manipulated. The Iron Bull says that she is the sort of people who like to follow orders but not to give ones. And I'm completely agree with him. Also, if there is a problem, she will go and solve it herself, she won't want to sit on the throne waiting for her people to solve everything. She also seems to be upset when she is chosen to become a new Divine. So I fear that someone like Vivienne for example will be able to control the new Divine.
Leliana takes a big risk but she'll win a lot if she is successful. She is a better person than Vivienne and she thinks not about herself, but about people including mages who are people too. Like Cassandra does. But it is very difficult if not even impossible to manipulate Leliana. She can handle all this political games either killing her opponents or talking them down. And I think that Justinia would want her to take this place. Many people say that Leliana's endings are too bright and lore-breaking, but it's complete bullshit. What about maleficarum and rogue templars? It'll be not easy for her to deal with all these things and to protect the innocent people. And there also will be some other clerics who won't agree with her actions. But the Inquisition was created to protect Thedas and it'll have to deal with all these problems like evil mages and mad templars. Leliana's epilogues are too "good" because they don't tell us about all the consequences. But I'm sure that the Inquisition will help her to build the world without fear and discrimination. And it's also a good way to strengthen the Inquisition's forses with a new magi order if you prefer to conscript the rebel mages like I did. Southern Thedas needs to be changed because it's a bit rotten. I think that the best way to do this is to reunite Celene and Briala turning Orlais into a cultural giant without elves being so oppressed and to have Leliana on the Sunburst throne as a new Divine who kills the old system creating a new one. A better one.