Mage Trevelyan is my favourite Inquisitor for a lot of reasons.
My female Mage Trevelyan was specifically created to romance Cullen and the world state was that the HoF was a female mage, and we all know Cullen had a bit of a crush on her (with my mage, that was mutual, for as far as it went). Mage Trevelyan bore a passing physical resemblance to the HoF, which is what first got Cullen's attention (and, hey, maybe he's got a type, right?).
I played this mage as being quite moderate, very much the Aequitarian. The Ostwick Circle was known for being fairly sedate, not a lot of trouble, and her family had a lot of Templars in it, so for her, going to the Circle was not happy or fun, but it wasn't horrible. She got to visit with her family now and then and receive and send mail (it helped that her family are nobility, of course), and she sometimes used her influence to make things a little better within the Circle when she could. Nothing super political or anything, but little comforts and so on. None of the Templars in her Circle were horrible or abusive. They mostly left the mages alone (which is how it's actually supposed to be in the Circle system; the mages are not meant to be prisoners, and are supposed to have reasonable autonomy, and the Templars are supposed to just be guardians and not jailers). She went to the Templars for aid with the Breech because she absolutely refused to strike bargains with a Tevinter magister who shouldn't have been there in the first place. She also actually agreed with Vivienne that Fiona's motion to rebel had possibly the worst timing ever and Fiona had shown absolutely shockingly bad judgement in other matters, and so Mage Trevelyan didn't trust Fiona any more than she trusted the Tevinters. Plus she was horrified at what was done to the poor Tranquil, and didn't want to work with any group that would do such a thing (at the time, she didn't know about the Venatori, etc., but she had talked to Minaeve and heard about the way the Tranquil were basically abandoned). She felt like if the Inquisition allied with the mages, it would seem to make all of these incredibly stupid and/or immoral decisions seem somehow legitimate, and if she conscripted them, she'd be no better than yet another oppressor.
This Mage Trevelyan went through the game being fairly moderate about these things and ended up with Cassandra as Divine, as you might expect.
My other Mage Trevelyan was male and was very much the Libertarian, quite anti-Chantry and anti-Circle. When he had to leave his family for the Circle, he felt unfairly imprisoned and abandoned, despite the occasional contact and letters from his family. He resented that what he saw as his natural place in society had been taken away from him simply because of some fluke of nature that made him a mage. He didn't hate his magic, per se, but he hated that people locked him up and treated him like crap because of it. He was a social reformer, even if it meant complete destruction of the Circle system and the Templar order. He did ally with the mages because he couldn't stand the thought of going to the Templars, especially after the show they put on in Val Royeaux with punching old ladies in the head. To him, it just reinforced the idea that Templars are jackboots. (He did manage to be friendly with Cullen, but only because Cullen had left the Order, and Mage Trevelyan came to respect Cullen's willingness to work through his issues and move in a new direction.)
This Mage Trevelyan romanced Cassandra and got Leliana as Divine, which suited him very well, indeed.