These are entirely personal opinions and observation, and not meant to offend fans of charcters.. ok let's start.
1. I think Riko is a much better Umi. Has better character delevelopment with the main character. Came from a distant place, Tokyo, arrived at a province town and eventually became close friends with Chika. Ah, and I'm not liking her because of the yuri bait - can just watch something like Ange Vierge if I need yuri.
2. One reason for watching this show is Yoshiko, simply because Chuunibyou is one of my favorites. No one in the original Love Live compares to her imo. The chuuni factor alone gets my attention. She still stands out even if only a few episodes are focused on her.
3. Considering You as a much better costume maker than Kotori. Again, same issue with Riko. Because You-sora has better character development - being alone with Chika at the start, just the two of them. It setup the anime as being a bit different from the original. And eventual drama near the end. The conflict of jealousy was not really explored in the original.
4. I like Dia more than Eli. A secret fan of µ's. I like how the writers made her serious sometimes, but funny when her real personality is out in the open.
5. Well. and this is just personal observation on our local community here. Aquors is totally trounced on by µ's. At Otaku Expo 2016, we stayed the whole day and I've seen not a single Aquors cosplayer.. but have counted at least 3 awakened maid cosplays of µ's complete with microphone props and mic stand (note: the awakened maid version is by far, one of the more expensive costumes), police version kotori, white day version kotori and others too many to mention. This scenario was repeated again at BOA 2016, seen ninja version of Maki and Nico, Umi awakened maid version that I've not seen at a convention before + others. The only Aquors cosplayer I've seen is a crossdressed guy with aquors school summer uniform ><. So far, few of my friends want to invest on an Aquors costume, but many have worked hard to save money for a µ's costume. We've just ordered a Kotori sore wa boku tachi version and we feel like we've invested in gold (can be sold again easily if we needed cash), because we view Kotori as a character that will be a popular cosplay for many years to come, similar to Chii from Chobits that people still cosplay even if so many years have passed already. Gonna do a Maki and Kotori photoshoot soon. Just waiting for Kotoribird to arrive.
Hoping that Aquors can have a season 2. Need more Yoshiko, You and Dia.