Honestly, some Sony XZ and Xiaomi Redmi devices were kinda nice in the past because even when they had a sealed battery they were still replaceable without super expensive heat plates.

Ethically I'd probably recommend a Fairphone 2/3/3+ in used condition, though they are somewhat clumsy. Ironically it's somewhat more private because the fingerprinting sensor never works in all of these models :D

In theory the Pixel 3+ devices would be amazing, but their resale value is just way too high for my cheap pockets. I set myself a limit of max 200 bucks for a used device, for both used laptops and smartphones and I never buy new hardware.

I'd avoid MediaTek chipset devices, because they have a known RootKit that can be easily exploited. Their CPUs have an undocumented root mode, and there's some apps and SDKs available that got leaked a while back.

My previous devices are now kind of ARM homeservers, because they either run ArchLinuxARM or PostmarketOS [1] on them, which is kinda nice and gives me a little satisfaction when I see that I can still use them for a nice tinkering purpose even without a battery inside.

One phone even runs my local mesh router with external USB Wi-Fi adapters, off-the-grid and solar charged. The display is used for the Web UI to manage things, which is also kinda nice. It's basically a fullscreen WebKit in kiosk mode.

[1] https://wiki.postmarketos.org/wiki/Devices

Samsung Galaxy S line fits as well.