I understand that the point of her rework and nerfs is to remove her "hidden power", but outside of not fixing that yet, there's another issue. Design wise, is there any advantages Sona has over Nami? Nami has more cc, is less squishy, and I'm going to assume is less mana-draining early game. Why would people (outside of Sona mains, which please Sona mains, explain your reasons) want to play Sona when they can play Nami?
Diostukos5 votesI have no idea, how, but I'd like it if Riot could keep her as a stance champion, while not having too much 'hidden power'.
Pika3105 votesThere is no reason to play Sona anymore, hence why I've switched over to Nami. She has: higher bases, more dmg, stronger heals, larger scalings, better mobility, more potent CC, lower mana costs, longer spell-range and an ult of greater impact on shorter cooldown.
Also, since she has higher AD, MS and mobility than Sona, Sheen and Lich Bane are much better utilized by Nami. Surprise surprise, they're items. Any champ can use them, they aren't Sona-specific. Contrarily to what a lot of ppl seem to want us to believe.
Raemnant4 votesI can play each equally well, but at the moment, I'm maining Sona. The reason for this is mostly because Sona is better at being a bully. I'm currently pushing past S3, so the people I get matched against arent the brightest of the bunch, so Sona's ability to poke and deal huge amounts of easy, almost free ranged damage as often as she can is a huuuuuuge advantage for me. I'm aware that such a thing isnt as effective in higher elos, mainly because I get matched with plats when I play normals, so I'm very aware of this, but here in Silver ranked, when I get my early 
for cheese, its total lane dominance. With correct positioning, strategy, and full abuse of Sona's many ability passives, her ability to zone an opponent is extreme. Undergoing such a tactic DOES attract attention from their jungler, but with wards, it doesn't even matter. This just means your other lanes have less pressure to deal with
SmokingPuffin3 votesSona is much stronger in lane. Sona lanes outtrade Nami lanes very harshly.
Sona's ult is a really reliable initiation, while Nami is more conditional.
Emmy Cha0s3 votesI've never lost to a Sona lane as Nami, it's too far 1-sided into Nami's favor that it's not even fair. With Ebb and Flow outranging Hymn aside, just a single bounce means Ebb and Flow solely by itself is stronger than Hymn and Aria** combined.** For every W I cast on Nami, Sona has to cast a Q and 1, maybe 2 Ws herself. Trading 70 of Nami's mana to force Sona to spend ~125-205+ mana forces her OoM and out of lane very quickly, especially considering Nami starts with higher base mana. Even worse, if Sona decides to get in close for some on-hit trading, Nami will almost guaranteed kill Sona. Making Aqua Prison easy to land due to Sona's predictable movement aside; Nami has higher AD and the on-hits from Tidecaller's Blessing severely outdamages Hymn's weak on-hit and the slow makes certain Nami can proc as many stacks as she feels safe doing so with. Hell, she can hand them over to the ADC who'll probably proc them even more safely. Even with Power Chord up, Sona loses every trade with Nami.
Chromatic Eagle1 votesBtw, this isn't so much my thoughts, though I am concerned, but this seems to be the consensus of the forums lately regarding Sona's nerfs.
Leblancs Boob1 votesNami is better at everything but I guess Sona just has a bit more utility lategame thanks to her auras. Still theres just no reason to pick Sona anymore
It Is I Emoto1 votesI feel like that Sona has become from a passive champion pick with alot of utility to a forced poke champ, because she got all that on hit damage things on her q, but as well recieved that hard nerf on her Q powerchord. I never felt before to build a lich bane on Sona, because the damage ratio on her Q was just fine and I felt like it was more important to build mana regen items, mostly athenes or mikaels, depending on what the team needed. Now it feels like that she needs alot of mana regen, thanks to her increased cost on her W, and even is needed to be spammed so that your ally or yourself get at least enough health.
Because of that extra on hit damage that Sona gets on each q cast, she's forced to throw a auto attack, so she won't waste any mana on it, putting her in more risk, wich is pretty dangerous for the squishiest champion in the whole league. I can even see why people complain about it, because it's probably extremly annoying if sona q + aa you and you can't do anything to block it, except you're yasuo or braum, and honestly it feels horrible to play like this too, since her bolts do on themselfs almost no real damage, and that I have to put myself on risk just to poke them.. yeah, it's pretty annoying.
Of course, a lich bane added to the poke-like play style is a benefit as Sona player, but that keeps turning her into a glass canon support, who relies alot on the onhit damage on her q+lich bane, and she has still no other way of cc, except her powerchord and her ultimate.