My golden standard as far as neutral IEMs was SE210. They just were junk mechanically, the cord got destroyed at the junction to the buds within like half a year of daily use. I got em twice replaced within the 2 year warranty, all thanks to the awesome local Shure support!
SE215 and SE315 that I've had after have both been greatly inferior. SE215 was as far from tolerable as possible. No midrange since bass was way way too dominant. In addition, the clearly audible strong shrilling resonance in lower treble got annoying and I could in no way live without equalizing it away by ear. As for SE315, they're clearly more neutral and lack that annoying bass dominance. Mids however are slightly too dominant, it's okay for vocalist sounds but in comparison to SE210, the 315s lack the neutral extension of mids on lower treble, highlighting even more the midrange dominant sound signature.
I've been playing around the UAPP morphit equalisations to the Shure IEM goals. The most expensive SE846 is far far away from neutral, even with the white filter. It's just a one dimensional bass monster. SE535 sounds very relaxed and neutral through mids and lower treble, maybe a tad pointed towards dark from neutral. I like the soft but okayish extended highs. Thou, the darkish signature still clearly distinguishes it from perfectly neutral.
SE425, out of all Shures sounds by far the most neutral of the bunch. High mids and low treble are stronger and more forward in comparison to 535, getting 425 rid of the darkish signature of 535. Thou highs feel less extended, and due to that fact the low treble seems to almost be too forward. I'd bet the total signature would sound less forward and softer if 425 just had more extension in upper highs.
Out of the Shures, 425 seems the closest to the neutrality of 210. It's so long since I had 210, but from what I do remember, the low treble was equally as revealing amd forward (like neutral should) if even more, but highs I think had more extension, giving overall more neutral and softer feel to highs on 210 than 425. But regardless, SE425 seems the new neutrality king so I think I'm now very close to ordering LG from my operator and later on switching to SE425, so that I could live without equalizing, and get full MQA hires signal out of V30!
Edit: V30 ordered! I'll probably get it on Wednesday or Thursday. A thorough listening comparison to HTC 10 will follow probably in a couple weeks, with/without morphit eq and obviously on/off comparison of full MQA decoding on V30. Cannot wait to test MQA!