I think all this speculation of whether friending or rivaling is the better thing for Anders is complete metagaming.
In the game, your character simply doesn't know... whether because they want to support a friend or because they support his viewpoints, they choose to help him at every turn. Or maybe they choose to help him sometimes because most of his requests have to do with helping people, helping mages.
If your character does not agree with his viewpoint or what Anders is (o.O abomination, grr stuff)... then they question and disagree at every turn.
What he becomes in interactions is a reflection of that... the more you disagree, the more you incite his anger. And in romance, he loves you, you don't agree with him, he struggles with all your questions and sometimes the anger takes over. You're bumping heads with him on everything he holds true or dear. He will react. And his anger is no longer Anders' (from Awakening) anger... it's this new person's anger. This new person that is both Anders and Justice, and neither.
On the friendship path... for 3 years he tries to stay away from the mage revolution. But the abuse keeps pushing and pushing and pushing at him... and he cannot sit idly by any longer. He doesn't have that self-preservation to just run away from it all anymore, which he had in Awakening. His humor and his shallow approach were his way of avoiding the bigger issue. He doesn't have that pretence any more.
So what's best for Anders is best decided on the experiences and opinions in game. To disagree with him vehemently just because metagame you think it's best so you can attempt to keep that old Anders part more separate or not... I don't know, it seems crazy to me. If your character disagrees with Anders' viewpoints and solutions, you react and he reacts to that. Simple as that.
As someone said many pages ago... in the end it comes down with whether you agree with Anders or not. And that's what it is, really.
And it's difficult to imagine the point of trying to convince someone who sees Anders justification that disagreeing with him vehemently and causing him blackouts is good for him.
In the end, I see my character as being friends or lovers with Anders because she appreciates who he is NOW.
My warden loves the silly old Anders, but my Hawke never met that guy. Hawke met this new Anders, for better or for worse... being rivals, friends or lovers is all about Hawke's opinions and feelings about Anders, the mages, the templars... the whole situation.
Pfeww, long rant. I apologize for the length. I'm just not understanding the need to keep going back and forth "rival romance is better", "no, friend romance is better"...