Well, for starters, Aveline claims to be in favor of following the rules, but she bends them when it suits her. A few examples of this are her support of murdering Kelder, the time when she mentioned killing slavers rather than arresting them in a banter with Fenris, and when she insisted that the elven viddathari be punished under Kirkwall's laws even though she didn't bother to investigate the rumors of sexual assault on the part of city guards. She also disapproves of Hawke trying to earn money from quests even though she actively blocked Carver from joining the city guard. I could understand not giving him a recommendation, she actively prevented Carver from having a steady source of income in the only thing he was good at, pretty much guaranteeing that the only way the Hawke family was going to make it out of Lowtwon was to risk venturing into the Deep Roads...
Anyway, that's enough about Aveline... suffice it to say that she is not a team player and she seems to need to be in control of everything and everyone around her. That's fine if you are willing to do things her way, but if not, she simply can't be trusted with authority over the military branch of the Inquisition...
But you are right that everyone has some kind of bias in these games, and Cullen is no different... either way, I'm glad Aveline isn't returning. As much as I liked her, her attitude got on my nerves sometimes.
Ah that's right, I forgot about the elven viddathari. That's a fair enough point
As for the Fenris banter, I can't remember that one at all. So I'll hold my judgement on that.
As for Kelder, however, I thought it was presented to us that the magistrate was Kelder's father? And that he had been abetting in Kelder's murder streaks of elven girls? So if Aveline had arrested him as you believe she should have, he simply would've been whisked away and allowed to continue his madness. Furthermore, he asks to die. He doesn't want to deal with his madness anymore. So I think Aveline is perfectly justified in killing him on the spot.
I can definitely see how she can appear domineering and have a need to control things. I still don't see how Cullen is more qualified, however, He has absolutely zero experience in building up an organization. He has always had the Templar name to back him up, along with soldiers who had been trained for years under the Templar doctrine. The Inquisition, while it is an old organization in terms of it's name, it is building itself from the ground up in terms of recruitment and training.
Furthermore, Cullen's only experience in actually controlling the Templars (after years of sitting blindly behind a madwoman) was in cleaning up Kirkwall. Granted, he would've had to deal with riots and instability, but it's one city. He isn't dealing with one city now. He is dealing with nations, with armies, with established organizations. You need someone who has dealt with other organizations that might be more experienced your own (Aveline and her guards against the Templars), and you need someone who can build up their own group into a powerful player. Aveline could have done that. I don't believe Cullen has the qualifications to do that. (Edit: I suppose a counter argument to this would be that Aveline has also only operated within the confines of a city as well, which would be a fair enough point)
However, it is a moot point. Obviously Cullen will do all of the above, because he is the military commander, and Aveline is not. And I doubt I'm going to convince anyone who doesn't like Aveline (or doesn't believe she would make a good commander). Doesn't change that I think she would be. Oh well.
To cut a long story short, I'm going to be biased towards Leliana and Josie 