I would really love to keep Loghain around but in Dragon Age: The Stolen Throne, Flemet tells Maric about Loghai n "keep him close and he will betray you, each time worst than the last" and the last betrayal we saw him doing was abandoning the field at Ostagar and naming the Grey Wardens murderers while trying to sell slaves, assassinate both the Wardens and Arl Eamon.
As a dead man, it's a little hard for Loghain to betray us but if he is a Grey Warden AND leading the Southern Grey Wardens then who knows what he could do, I love Loghain more than most people but even I must say that he is bloody destined, by Mythal of all people, to betray the Protagonist.
I just wanted to mention this but I do love Loghain and I have kept him alive in three of my playthroughs - however I normally keep Alistair around. I would keep him around a lot more if he didn't sell Elves to Tevinter, try to murder Arl Eamon and, of course, getting the King of all Ferelden murdered.
P.S
One of my favourite things about Origins is that some people may not even know that you can have both Loghain and Alistair(kind of) by having Alistair marry Anora and then you can have Loghain as well, keep in mind - you must have Alistair hardened.