Here's a match that I labeled as one of the "Big" matches. I wanted to actually illustrate Sanae and Utusho, but I don't really have time, but that's besides the point. Let's cut to the chase....
Faith vs. Hell
Sanae Kochiya vs. Utusho Reiuji
Sanae Kochiya
Pros: Is a direct contrast to Reimu in almost every possible way, As in dedicated, devoted, hardworking, cheerful, friendly personality, originally from the outside world, expresses knowledge from the outside world, nice attractive body (including a decent chest size in contrast to Reimu's flatness) and also has strong faith in her gods. Big anime Otaku fan, (especially in mecha), sic-fi fan, nice color scheme, shrine maiden, formally a school girl, not held back to open up to new ideas leading to her character have infinite possibilities both in her character and personality. Amazing major character potential
Cons: potential psychotic side (as seen in route B of UFO), bully to Kogasa (as seen in some fan art), some fanon portrayal tend to take advantage of Sanae's looks to attempt to take her down a peg so she doesn't seem all that perfect (AKA slut)
Utsuho Reiuji
Pros: Hell raven with the power of the sun, long black hair, large wings, destructive power, awesome spell cards (WARNING! WARNING!) quite furious when she wants to be, large cape with the galaxy designed within the inside, unique design in term of how she represents Yataguratsu (cement foot, atoms and arm cannon), having a cute,idiot, bird brained personality underneath that destructive power, "Unyuu~!", color scheme that makes her stand out with her design,great body (at least in fanon works).
Cons: some may find her destructive personality a bit much, same goes for her bird-brained side, some may find her design a bit over done (I know cause a friend found her unappealing for that reason alone).
Advantage: None, They're both even!
This is going to be one of those very big battles I've been waiting for.
On one side, we have a shrine maiden, who since her appearance has grown in popularity in the fan base, and has become a rather strong character in the Touhou Universe. As because of her she now gives Reimu serious competition because of her approach to everything, her looks, her behavior, her personality, everything about Sanae completely contrasts Reimu. Where Reimu is from Gensokyo, Sanae is from the outside world, where Reimu is mainly flat, Sanae is busty, where Reimu is laid back, and doesn't care much, Sanae is devoted and willing to help and try new things, where Reimu lacks a god in her shrine (since the PC-98 days), Sanae has 2 gods. Really I could keep going on about this for a while. But long story short: Sanae is pretty much the Luigi as Reimu is the Mario. Same can even apply to their color scheme.
Also Sanae also has many strong points that connect to the fan base as well. She obviously has develop from what was once a devoted girl to becoming a girl who comes to now be held by logic (and make silly names for spell cards) then later we get to learn about her Otaku geeky side. Really, this has gone places few character in the Touhou universe go. She's practically the living embodiment of an Otaku boy's fantasy manifested into a game.
The only thing Sanae has that may even make things hard for her here mainly derive from UFO and her memetic fan base. Which center around her becoming an aggressive youkai bully, and being portrayed as a slut (thanks to the western fan base) But those are even sometime turned into an advantage even for her. So who knows?
On the other side we have Utusho the hell raven, known to be the only Touhou character who actually came close to having a villainous personality when she first appeared, but was very notable for her amazing design, her character, and her amazing portrayal of spell cards.
Utusho mainly has a strong edge in this competion mainly for her looks and personality along with how she was captured in SA. Her spell cards through SA were probably considered mesmerizing and awe-inspiring, starting with the warning signs and the alarms that would ring out before she would start hurdling gigantic suns at you. Follow that up with her great design which consisted of her being dressed in a white blouse, a green skirt, large black wings, long black hair, a giant cape with the universe printed on the inside (that's alive according to Hisouten), cement leg and atoms on the other, an arm cannon and later on a great body from how fanon captured her design.
Then to top it off we even learn that despite her villainous and destructive personality she has in SA, that deep down she's actually rather simple minded to some degree which added a cuteness appeal unlike anything that had been seen before. And had a catch phrase that totally made her moe appeal concrete....
"Unyuu~?"
That's all it took!
Really there's alot going on for an SA character here who's only appeared a few times, but yet Utusho is one of the few characters that shown great promise in the Touhou universe.
The only thing Utusho has that might bring her down here in practically some of the same things that make her good, her destructive yet idiotic personality, and her design, some have claimed it may have been over done, but all subjective for debate.
So in truth, from what I seen, this contest is dead even.
It's going to ride on taste preferences, in character, personality and design that'll be the deciding factor on who'll win here.
As for me I'll give my answer on my vote:
Sanae, why?
Sanae is one of the few Touhou characters that has so much potential growing for her. As I said before, she's one the few characters that indeed grows as time goes on and it shows quite well. She has developed into a character that actually give Reimu something she never really faced before: Competition! And being that how contrast Reimu in every way almost make her really stand out in her character. And with each story she appeared in we learn more about her and her adaption to Gensokyo, at this point, she's pretty much now part of the major Gensokyo crew. And being able to accelerate all the way to 2nd place in the Touhou Saimoe competion in just the 3 years she's been in existence proves that she's gone far. She practically rivals even most of the major characters in Touhou with her development and I expect Sanae to continue doing this through the future of Touhou if ZUN continues with the route he goes....
Utusho on the other hand while she can definitely develop some more from her current stance, it's sort of limited, most of her character is set into stone already so there's really only so much I can see going on for her through the future compared to Sanae. Sanae is an open book with pages waiting to be written, and only in due time will we know just how much more we'll get to know of Sanae.
So yeah Sanae get's my vote due to her limitless moe potential that we know past, present and the possible future.