Too bad she's already miserable even before she's Divine. I can't condemn her to that. She's also not very political which could be damaging in the long run. Leliana both knows politics and is compassionate. Best Divine for me.
I bolded the important part. Leliana is the best divine for you, since the idea of who the best divine is is purely subjective and not objective.
To some, Cassandra would be the best divine for them, because like Captain Anderson, is not interested in politics at all and is instead focused on doing the job based on the principles it was founded upon. Others like her because she tries to reform the Seekers and Templars and root out the corruption among their ranks, and treats the root causes of the mage/templar conflict, which is something many pro-mages in the debates over the years wanted more than anything, more oversight and less power to the templars. But some people don't like her because of those very reasons.
To others, Vivienne is the best Divine because she offers mages more power and responsibility than ever before, and her position as the first mage divine is a sign of progression. Others like her because she comes down hard on those who would cause dissent. Some people who wish to restore the status quo probably don't like her because mages advance so much, and I've even seen one poster say her becoming Divine is the first step to a new Tevinter because it gives a mage direct political power.
And others, like yourself, see Leliana as the best Divine because she's so open, compassionate and sees the very real prejudice that the Chantry engages in and pretends its above. They like how she'll disband the Circle, let elves dwarves and such become priests instead of limiting to humans as has been done. Others don't like her as Divine because they think she's too radical, or she makes to big changes way too fast, or don't like how a hardened Leliana will assassinate, blackmail and so on to get her way, making the Chantry's steps run red with blood from her opponents, meaning the more conservative voices in the Chantry.
It isn't possible to say one Divine is actually any better than the others. Some Divine's are better for what you as a player want to see, but if another gamer wants a different outcome, they have the option to support another Divine who'll support something they like. It's strictly subjective.
But since they all end up with the name Divine Victoria, it'll be easy to say "Victoria says this about what's happening" in future games as they become a far off figure, and their direct actions are things we will only hear about.