I think the decision here depends on how much stock you put in the mage/templar subplot. I don't care for it so the mage Inquisitor/Templar Cullen dramatic tension really doesn't appeal to me - other players here in the thread are all about that storyline and their whole romances hinge on that conflict. It's all different approaches, so it's more a matter of considering where you fall on that line.
The "immature, impetuous rich, spoiled, bad girl type rogue" more or less describes my Inquisitor I'm romancing Cullen with (there's a lot more to her than that, but it's a good start). I specifically chose a non-mage class because I wanted to give Cullen a more lightweight romance that didn't revolve around the same mage/templar drama that haunts every other aspect of his life; we know there's some manner of conflict in his character subplot anyway, so I'll be leaving all the tension for that. But with the more "bratty" personality my Quiz developed, I think it can be a really fun romance, Ser Frowny Serious Business and miss I-don't-know-what-I'm-doing. Mostly, I want to make him smile with my rogue. Get his head out of that mindset of constant vigilance and make him open up, allow himself to be happy for a change. I think a rogue with Cullen would be particularly good for him, because they fuel on fun and run life on easy mode, and he needs some of that in his life - but a warrior can also be interesting to roleplay, specially if she takes the Templar specialization and has that much in common with him.
But! If you prefer drama to easy riding, there's the mage angle to go for. I'd be mindful of how much you're willing to bend on that "staunchly anti-Templar" angle, though, because even though Cullen is willing to romance a mage, I'm not sure he's willing to romance one who is against everything he holds most dear. Since rivalmances are gone and positive/negative approval are back, I'm thinking radical anti-Templar Inquisitors will have to bend on their position as much as Cullen on his, or the romance might never take off. That's something to keep in mind.
I don't think any of us should make the decision for you. Think on what you want from the romance, which angle you'd rather explore, and it'll come to you. Worst case scenario, there's always that distant second playthrough to explore the angle you missed on the first. 
Yeah this was from a while ago maybe, but I'm a tad tipsy and I don't care. Also, apologies for spelling or owt.
Personally, I'm a bit of a drama queen. It's why I wanted my Seb romance to have ended angrily with the refusal to kill Anders, while still siding with the Templars. It's why I'm really excited for my third playthrough with my qunari Hissra, whose world state has Morrigan romanced, refused the DR and stabbed at the Eluvian.
But I'm not really a fan of mage templar drama, which is why my Elidri's Cullen drama I want to stem from her pro-Qunari views. My ideal ending would involve her actually leaving Cullen, (without any notice or anything for extra heartbreak on both sides), and joining Iron Bull in travelling to Par Vollen or something so she could join the Qun. I don't think it'll be available but I can dream.