Now I prefer the Templar side for various reasons:.
The Mage side does a poor job at involving the faction you are actually trying to recruit whereas Templars actively participate in the Templar plot.
I dislike Time-travel storyline in fictions in general. It's a bit cliche but I was really enjoying the Mage mission until Dorian told my character : "We have been transported into the future!". Then I become really detached from the plot because I know everything I'm playing is in a future that won't happen because of course, we have to fix the alternate timeline.
On the plus side, the music and art direction is really well-done in future Redcliffe castle and you get a cameo of the Ferelden ruler(s) (but it's very short).
Now on Fiona:
On the Templar side, I never really saw the appeal of Ser Barris (like Fiona, no strong feeling one way or the other) but maybe that's because I conscripted them so I didn't get his wartable mission?
I did prefer Calpernia over Samson, but from all I had heard about her quest, giving more insight on Coryfish and all that; I was really disappointed, you don't learn THAT much TBH. Still, better than Samson, and a far more memorable character once you reach the Well of Sorrows.
I like Cole, so I don't like missing on his introduction at Therinfall.
The Envy demon is both creepy and funny.
So yeah, Templars, unless I reroll a mage in the future.