I do enjoy the Friendmance better with Fenris, than the Rivalmance. Having done both though, the two varieties can be role played believably. At least from my perspective. The Rivalmance with my Tyrel Hawke and Fenris, was a great RP experience, but if anyone remembers the epilogues I wrote for some of the Hawke/Fenris pairings...that one didn't end terribly well (still better than Sad-sack Hawke...and she WAS a Friendmance...hehe!).
My very first play through (when I thought for sure I would romance Anders) was very green. I tried to play my spritely red-headed rogue/archer, very honest. Even then, I still managed to max Fenris' friendship out by the last quest in Act 2 (yup; he gave me the remaining 10 points I needed, by agreeing to duel the Arishok). Here is where I took hits:
1) Let Fenriel go to the Dalish
2) Defended my sister during right after Danarius' mansion in "Bait and Switch".
3) Didn't agree with the circle when first visiting the Gallows with Fenris in Act 1.
What made up the difference was that Wayward Son gives more F points than R, if you kill slavers (which I did, and always do....except once), not agreeing with blood magic when picking up Merrill, taking a certain path in the dialogue when speaking to him at his mansion, all the points you can garner by truly helping in 'A Bitter Pill', his gift in Act 2, and finally the Arishok confrontation. And now, you can also get more points in Legacy (and interestingly enough, you get them for Anders in the same way). I will admit, that I did NOT have Fenris with me during "Act of Mercy", and that was just sheer luck. I was trying to play a few characters that I hadn't really been using much of at that point. Had I taken him with me, then it may have taken me to Act 3 to finally max him out.
As for liking the Friendmance more, I admit I find it more endearing. I especially like it with my mages. The one line in Act 3 during the Rivalmance, and it may be more indicative of Hawke's personality, that really gets under my skin is when Hawke says, "We're not exactly Friends, Fenris." I know this can be viewed in more than one way (friends vs (ex)lovers), but it makes me grimace. It worked ok for my Tyrel Hawke, but I still feel it was because of the way I RPed that Hawke. There is also the general sense of frustration that comes with the Rivalmance that just doesn't make it seem like a long lasting relationship. This is just MY impression when playing it, NOT that people can't role play it differently. But the bottom line is, BOTH paths have their fun, and their value for role playing.
Nowadays, when I Friendmance Fenris, I play honest to the character, which DOES mean their is some metagaming. Simply put, if I RP a Hawke that is trying to maintain an accord with Fenris (whether it's right or wrong doesn't matter...it is realistic for SOME people/characters to be...hmm..overprotective at times, with those they care about), I won't be dragging him with me on "Act of Mercy", for example. I also play a lot of Hawkes who's position and personalities change through the different Acts. As much as Hawke can be an influence on his companions, I allow for RPing of some Hawkes for the companions to influence her/him. So this means that even if a certain Hawke decides to support the mages in the end, they may not have actively participated in liberating all mages in previous acts/quests. Different Hawkes, different personalities and choices.
That was probably much longer than it needed to be. Sorry for the tl;dr.