Android

Fairphone: repairable and modular, microSD expansion slot, support custom ROMs well, mobile Linux support is great, BUT no audio jack

Their Fairbuds XL are pretty good value with easily replaceable batteries

Sony Xperia: good custom ROM support, excellent cameras, audio jack + microSD card slot, BUT flagship "1" series is very expensive

Google Pixels: plenty of custom ROMs, including GrapheneOS, BUT poor battery life, overheating issues, not great value

Get Pixels used! You'll save money and will avoid financing Google!

Shiftphone and Volla: both have excellent custom ROM support and are unique devices BUT generally poor value purely based on the hardware specs

Shiftphone is repairable and modular, like the Fairphone, while Volla treats mobile Linux as a first-class citizen, so they are about equal footing in my opinion

HMD: Decently repairable, relatively affordable, BUT not the best custom ROM support, mostly unremarkable

(I do not recommend devices below this point for most people)

Motorola: headphone jack, usually very cheap, BUT not the best custom ROM support, mostly unremarkable

Motorola is only this high because of the headphone jack

Nothing: gimmicky while being less repairable, forcing AI into their devices (e.g. "Spaces" button that cannot be remapped, LLM-generated widgets), poor custom ROM support in their newer devices

Vivo and Xiaomi: best cameras (big sensors and extensive software processing), excellent battery life, BUT poor software experience with few devices supporting custom ROMs

Xiaomi has the advantage of a wider hardware selection across all price ranges

I have personally experience with the struggles of OriginOS (Vivo's spin), I would not recommend it. It is tolerable, but incredibly annoying and quite bloated too

Oppo: excellent cameras, great battery life, BUT poor software experience, poor custom ROM support

Redmagic: gaming phone, large battery, BUT poor software experience, not great if you want a regular phone

Samsung: OneUI is nearly as bad as the likes of HyperOS, lacking hardware, poor value, no custom ROM support

Asus: they suck in seemingly every category, poor software support

Some of their older small phones could be saved by custom ROMs though, but they are harder to find!

If you want to run a Chinese OEM device for the cool hardware, I would recommend a custom launcher (like Kvaesitso or Lawnchair) and the use of ADB to remove all the unnecessary bloatware. You could do something similar with Samsung devices too (you don't get good hardware on Samsung so I would avoid buying a new one, but if it's what you got, try to make it a bit nicer by debloating it!)

One more thing: if you are interested in emulation, you are better off getting a device with a Snapdragon chip since those have the best custom driver support. Many of the Chinese OEMs use Mediatek chipsets, and Samsung infamously puts the Exynos chip on most of their devices. Pixels use the Tensor chipset, but if you are getting a Pixel you probably aren't doing anything high performance anyways haha. My (Vivo) phone has a Mediatek chipset, which is more than powerful enough, but it can't do Switch emulation because of graphics driver issues. 3DS played fine though