It largely depends on when Logain knew what.
We know:
1) the battle at Ostagar is not winnable. The head guy said so!
2) Grey Warden's are required to end the Blight
3) Logain made a crown for himself
4) Cailin was corresponding with Orlais.
To point one, the question revolves around when Logain determined that their forces could not win. In an era when military commanders worked largely based on estimates, I don't think the Fereldan forces could really have known just how large the Darkspawn force was.
If Logain knew before the battle, then he is a regicide and a traitor. A Usurper and betrayer of Fereldan. It was his plan, and he knew of the king's behavior and tendency to be on the front lines. He wanted Cailin on the front lines, and got exactly what he wanted.
If Logain suspected Cailin was corresponding with Orlais and wanted to prevent any possible union with Orlais, then he is everything above but with some possible justification other than greed and pride.
If Logain didn't realize how large the force arrayed against them was, and not until the battle commenced truly understood how large the darkspawn horde was, then he is merely an opportunistic sociopath who felt justified rewriting events to suit him.
2) To my knowledge, we do not know if Logain was aware of the importance of Wardens. Most of the evidence suggests he didn't, but we don't know for sure. You can't really blame the man if he didn't know of the importance of wardens.
3) is pretty damming in my eyes. Regents don't need crowns, nor is it appropriate for them to wear them. Either Logain just says "You know, I'd like to be king" or he planned to betray Cailin all along.
To keep this fairly short. IMO Logain was a dirty traitor, who plotted to leave the king for dead. His actions threatened the entirety of Ferelden and he should only be allowed to survive the Landsmeet if you intend to sacrifice him to kill the Archdeamon. The evidence suggests that he was planning to remove rivals and the king should the opportunity arise. His goal was to be king, and he would be king even if the consequence was being the king of a dying, blighted land.