Since I started the discussion I will start myself ofc =P
After loads of thinking abut it I would actually chose Gaspard.
I don't LIKE him, or think he is right, but I can actually understand him the most.
Let me explain:
I absolutely despise the so called game and think it should be stopped.
The game is the embodiment of the worst parts of politics and, truth be told,
I'm not really patient enough for politics to begin with (to use MTG terms, I
tend to be red-white =P).
Celene stands for the game. She uses it, she is a master in it and I always get the
feeling she actually ENJOYS it. The empress wants change, true, but the change
she wants is not the change I say is the most important.
She wants to allow the elves to become part of the elite, but this is something
that will only be accessible for a part of her subjects (including commoners)
Not everyone can b a merchant (and be successful) and not everyone can be a scholar.
She doesn't REALLY want to change the system, she only wants to stop "discrimination".
But seriously, if you are a hungry commoner do you really care if the person that profits
from your work was born a common human, a slum elf or a noble? No, you will mostly
care about being hungry -and Celine does nothing against poverty or such, thus her
reforms are uninteresting for the majority.
About Briala, I understand her reasons and her goals. But my problem
with her is twofold actually. First thing:
I don't want an elven nation. I want to achieve a position that doesn't care about race.
Since I'm an isolationist myself I completely understand the sentiment of wishing to be left alone,
but if you can't leave the "world" you have to arrange yourself with it and the only way is to
find a way to live together. It will be hard, true, but it is the only working way.
But the other problem is the bigger one: I completely and utterly hate her plan.
Prolonging a war is WRONG. It just increases suffering and -sorry about that- I don't
care that elves hat is bad, making humans suffer for elven freedom is something I can not forgive.
A crime is a crime, no matter if an ******* or an poor victim commits it. Can I understand the victim?
Yes. Do I dislike the ******* for doing it and am I more sympathetic towards the victim? Absolutely.
Does this change anything? Hell NO, wrong is wrong. ..So no matter how much I sympathize with
her and her course of actions I could never condone them... I'm sorry about that =/
And no to the last one.. Gaspard.
He wants what he thinks is best for Orlais - I can understand that.
His dislike of the game is something that I share and my favourite moment
in the book is when he tells Michel that he doesn't care about the fact that Michel
is a commoner and an elfborn, since he thinks the (former) champion is the ideal of
a chevalier...
Does he do bad things? Yep. I also think he goes to far and is too ambitious, but
I also say that he is the only one that -no matter how problematic I think he is- I have the
most hope if it comes to him... I get the feeling that he agrees with my personal concerns 
(I'm totally aware that I'm biased, but I hope to learn if anyone gives good arguments =) )
About the characters.. If I would play an orlesian noble I would favour Celene,
because s/he would understand the game as something useful (instead of despising it).
A mage character may favour her, because mages are usually better educated compared
to commoners, so Celenes reforms would be more interesting.
A dalish character might favour Briala, since dalish don't care about humans and she is
the best bet get back to being Elvhen..
A Vashoth character (as well as any warrior character) would most prob. favour Gaspard,
since he is a popular military figure. Plus the military is organised, while the game is more
..chaotic in nature ^^
Well, I truly hope this thread catches your interest =)
*edit: Dammit, I was too slow xD I lost my chance to be the first =P