It was interesting to see why the older members loved their favorite idols. I didn't realize voice was valued so much. I've listened to all the idols a lot so I enjoy listening to all of them. Personality is important to me too.
Rambling about Chihaya incoming.---
While many people and official materials refer to Chihaya as stoic, I think that refers more to her idol side. Personal wise I'd say her being awkwardly cute is a trait a lot of people like.
Chihaya is considered the hardest to deal with, or used to be before tension was removed, but I found it harder to please Iori personally. Maybe it depends on the person and how well they know that idol.
I've seen a lot of misunderstandings about Chihaya, a lot coming from the anime, even in this forum. I'd be glad to respond to any questions you have about this.
OFA mentions how Chihaya as an idol and Chihaya as a person are pretty different, and thinking upon it I think that's true. We're mostly shown the idols personally so it's easy to forget that the in universe fans don't see the idols like we do.
As for Chihaya's voice I always liked the power in it and how she sings long notes. In OFA I'm not sure if it's by chance or related to the plot, but I felt that her singing has improved. For example her version of 99 Nights combining softness and power, while her Visionary being pretty cute. Before OFA I had assumed that her Eden would be my favorite.
https://www.youtube.com/watch?v=D6M3t1rHeJIhttps://www.youtube.com/watch?v=phqRwKlTpOoChihaya comes off as mature for her age, at times I used to forget that Haruka was older than her. However she does have an immature side to her (although it seems like this isn't shown as much in later works). For example when Chihaya says that she's enjoying her life as an idol and student Producer suddenly responds that he'll leave her and she responds like this.
http://www.mediafire.com/listen/ra4dpvl7hrnk74k/I think Chihaya's story is pretty relate able to those who have dealt with divorce or loss of a loved one. While it is obligatory to mention it as Namco is appealing to newcomers as well, it's actually been mentioned less as time goes on (her main OFA route reduced it down to one sentence even).
Even if you don't relate to her story, Chihaya tends to ponder and over think things even when she's grown as an idol, and I think that's another relate able quality she has.
Interesting to note is that her VA Mingosu originally didn't like Chihaya that much when she auditioned for idolmaster. She was shown a black and white image of Chihaya in plaid and sandals like this.

She thought "Who would want to pick someone like this? Wouldn't someone cuter or girlier be better?". Originally Chihaya was going to be a loner, but it was Mingosu who suggested that Chihaya's main trait be "likes singing" before they fleshed her out. Something to note is that not only Ohayou Asagohan, but pretty much all of original arcade recordings were sung differently on purpose. Mingosu would sing songs like Watashi wa idol cutely, and would be told "You need to sing it more coldly, Chihaya hasn't opened up her heart yet" or along those lines. Of course eventually Mingosu warmed up to Chihaya and now they're really close.
Interview Source:
http://www.famitsu.com/news/201011/19035791.htmlI think another reason why Chihaya seems like such a love or hate character is due to how she changes throughout her routes. Even the original arcade players didn't like Chihaya that much on lower ranks, it was people that got her to C Rank or above that were encouraging others to do the same. Unlike now people couldn't just look up videos of the commus online either. In a sense Saihyou is similar in that it starts out gloomy but turns into a positive song.
For example
iM@S 1 E Rank:
https://www.youtube.com/watch?v=R6LjE-R_3UEiM@S 1 AB Rank:
https://www.youtube.com/watch?v=n7xfRO9q004OFA Evening Commu:
https://www.youtube.com/watch?v=JQNl3Zzb53gOFA Morning Commu:
https://www.youtube.com/watch?v=U-_h15FQZjsI enjoy how passionate she is about music. I think her final imas 2 text was adorable in how it combined her indirectness with her knowledge about music.
I've always kind of viewed Miki and Chihaya as opposites, and that's why I think them being rivals was interesting.
Miki - Talented but lazy (not including Awakened Miki), quick to quit when things don't go her way, very open about her feelings, has lots of friends, her parents are together and her sister is alive, outgoing,
big breasts, etc.
Chihaya - Talented but dedicated, only quits when it's the last option, very indirect about her feelings, has no friends outside of 765Pro, her parents are divorced and her brother is dead, introverted,
small breasts, etc.
I think Chihaya and Haruka being designed together helped them get along so well. They both have their positives and negatives with each other. For example they can fight over things like Chihaya being too closed off or self centered, while Chihaya gets upset when Haruka says she wants to be more like Chihaya. Haruka admires Chihaya's singing voice and knows how she acts well, while Chihaya admires Haruka's positiveness and enjoyment of things. They both enjoy music but in different ways. Haruka helps get Chihaya into some of her hobbies like baking, while Chihaya helps Haruka become more informed about music by helping her with singing or giving her recommendations.
One of my favorite stories is Eternal Prism 3 as it pits Miki and Chihaya against each other as love rivals and unlike SP has an interesting ending.
http://www.mediafire.com/listen/5ctiumy12hoo0hl/It also explored things like Chihaya being afraid to love Producer due to having lost someone she loved in the past.
http://www.mediafire.com/listen/zm4oggebbr49rf2/Speaking of Chihaya being indirect, something to note is that if you ask her about something romantic directly she'll get flustered or mad, but if you ask indirectly she'll start mentioning it on her own. Another hint is that Chihaya doesn't like excuses or jokes when she's being serious about something, it's best to be honest with her rather than trying to soften the blow.
A trend I noticed in the serious drama CDs involving Chihaya is that her onemindedness and quietness would get others like Haruka and Miki angry at her for being so selfish and unfeeling.
http://www.mediafire.com/listen/sgho8cazl651eoa/http://www.mediafire.com/listen/tvj3fbs61bb3wch/http://www.mediafire.com/listen/cz73fuozwabcd37/By the way Chihaya losing her voice was done in New Stage 03 years before imas 2 or the 2011 anime released.
http://www.mediafire.com/listen/q1c94f4bozfh5wq/Sorry if this came off as completely unsorted, I was adding things as I thought of them. All the mediafire links are audio clips of the things I mentioned.