I generally prefer picking Alistair.
He has proven that (despite the claims frequently makes throughout the game) that he makes a great ruler loved by all of Ferelden.
Plus, with Anora, she's a woman who potentially backstabs the Warden not once, but TWICE, for generally arbitrary reasons, despite knowing what's at stake, and seems to assume she can simply get away with it.
I bet she'd betray her own kingdom and subjects if it benefits her or keeps her from taking responsibility for her mistakes. Is that the sort of leader Ferelden needs?
With Alistair, you know you can trust him that you'll be protected under his rule. Plus he's more tolerate of mages and elves than most humans in Ferelden are and if you pick him, he takes some steps to improve lives for both groups when Anora I don't think has ever lifted a finger to so much as keep the nobles from bullying the Alienage Elves.
So you know with Alistair, he'll be taking action not just to keep the people of Ferelden safe, but also to improve their lives in whatever way he can.