I'm pretty sure the Hat wanted to sort Hermione into Ravenclaw but, like Harry, she picked Gryffindor. It's been a while since I read the books, so I may be misremembering.
Oh, I've read the books fairly recently. It's true the Hat's first choice was to sort her into Ravenclaw, but it also sensed a small spark of courage/adventure/defiance in her, and ultimately chose to put her into Gryffindor on account of that spark. (It helped that that's the House she wanted.)
I think it's worth noting though that while the Hat takes people's desires into account, it doesn't base its decision entirely on them. According to Pottermore, the Hat also sensed a bit of courageous potential in Neville (buried underneath it all), and wanted to put him into Gryffindor to nurture it. However, Neville was intimidated by Gryffindor's reputation and wanted to go into Hufflepuff instead. The reason the Hat took so long to sort him wasn't because it couldn't decide, but because it took so long to bully convince Neville to accept being sorted into Gryffindor. If it just took his desire into account, he would have been sorted into Hufflepuff in ten seconds and that would have been that.
I think Solas (on topic!) would make an amazing Ravenclaw, but he has just as many qualities that make a fantastic Slytherin.
Yeah... That's kind of another problem I have with the Sorting concept. Most people don't fit neatly into little boxes or stereotypes. Most people are more complex than "You value wisdom and knowledge, so go to Ravenclaw," or "You're ambitious and cunning, so go to Slytherin."
It's also complicated by how the Hogwarts House system works. They get students young and teach and raise them into the kind of people they'll be when they go out into the big wide world. Since the tween and teenage years are so vital to their personal development, the Sorting Hat examines their potential and puts them into the environment it thinks they're most likely to thrive.
We don't see Solas as a child or young man, so we don't know how he would have thrived had he been sorted young. We see that he values wisdom and knowledge now, but that could have been shaped by events in his childhood and young adulthood that we haven't seen. He claims he was cocky, hot-blooded, and eager for a fight when he was younger, which, for all we know, means he would have been eager to be sorted into Gryffindor at that age. He also hints that he had been very ambitious and out to prove himself when he was young, so maybe Slytherin? I feel Solas implies that he now values wisdom, introspection, and self-reflection at least in part because his illusions of grandeur blew up in his face, and so now he's been humbled and seeks self-betterment for its own sake.
Now that I think on it, it's hard to tell. =(