I've been using a Sony Xperia Z2 (6503) with CM12.1. Unlike all my previous phones with CM, outgoing audio quality during calls has been a constant issue, and kept being an issue on the replacement Z2 I got.
So I'm replacing it.
The Z2 and Galaxy S7 will probably give a good idea of the kind of smartphone I'm after, but there's a load of other phones out there beyond those two. Desired features:
Size/form factor/screen: standard high-ish end Android smartphone. Large smartphone or smaller phablet sized. Roughly, 5.2 - 5.99 inch screen (ideally 5.5 - 5.7 ish), and up to about 79 x 170 x 9 mm. I don't need ultra-high res on the screen though. 1080 HD like the Xperia or even a bit less would be fine.
SoC/RAM/ROM: The Z2 I'm used to has a Snapdragon 801 (MSM8974AB quad Krait 400 2.3 Adreno 330). I'd like to improve on the CPU side if possible as we're a few years on from this generation, but open minded what to go to. 6-8 cores? 64 bit? I'm open minded and this isn't essentsl, I can "make do" if needed. Ram - at least 3GB (2GB isn't enough). Rom - the usual 16 or 32 GB is fine. Graphics - I don't game so open minded.
Phone/data bands: primarily UK but able to handle some international. At minimum, GSM, and for data, GPRS/EDGE/HSDPA/LTE (UMTS 900 (8) / 2100 (1), and LTE 1800 (3) / 2600 (7) / 800 (20). Ideally good choices for EU and USA as well, and ideally a recent version/speed for LTE (Z2 has cat 4).
OS: can load custom roms + TWRP, with a stable build of some kind (official or otherwise) out there. Not bothered if it has official CM support as long as there's an AOSP/CM style community rom without major issues that's good to go.
Audio: Good clear audio and reception on calls, whether held to ear or on speakerphone, is a must.
Other features: most phones of this kind will have the usual WiFi/Bluetooth etc, so I'll skip those. A lot of other details aren't important to me so I've left them out as well.
-- Needs SDcard of some kind, a micro or C USB slot,
-- IP x5+ rating for use in wet conditions (ideally with a screen that isn't completely hopeless in rain - I've read somewhere that some phones have a screen that detects touch moderately well even in rain),
-- decent resilience (gorilla glass or similar, robust build),
-- headphone socket that doesn't share with USB (so both can be used together),
-- good camera for difficult light conditions (fast focus/good sensitivity is a bonus) + front facing camera, that can do 720HD or better,
-- as much GPS capability as it can have (all the networks!).
-- Decent size battery/battery life, as I use it a lot for browsing/news feeds etc.
I'll be buying off EBay, as previously, so models that are readily found 2nd hand online are a good thing. My budget is probably around UK £ 100 - 200, but that's for a good bargain price and for a used phone in good condition up to a year or two old.
Ideally I'm after several models, to put together a shortlist of up to about 5 - 7. But if there's only 1 or 2 stand-out models, that's fine too. I'm open to reading the specs for more if there are any.