Since Android is currently the only choice of operating system that is even remotely Free Software and widely available, many people end up buying phones with this OS. The question that follows this decision is this:
Do people have experiences about phones that they can share, particularly regarding bootloader unlocking, rooting, repair and so on?
Actually we have some pages dedicated to that:
https://fsfe.org/campaigns/android/android.html
https://fsfe.org/campaigns/android/liberate.en.html
If you find anything amiss… feel free to complain loudly to help
fixing it (or to fix things yourself, that’d be even better :-)
Cheers
– t
Thanks for the links. I’m aware of those pages - isn’t this section of the forum named after that campaign? 
I guess I need to click through to the individual projects mentioned on those pages to see what hardware is supported. I was hoping for a summary, or just to hear some experiences from people who have recently bought phones to run Replicant or LineageOS.
@davidb maybe check which device is popular and nicely compatible with LineageOS and then buy one used. Especially considering the factors you mentioned, they will always be better for ones which are widely used. (The Moto G 1st gen I bought used years ago was quite good for a long time and worked without issues.)
If you must buy new for whatever reason, consider a Fairphone. I’ve been running LineageOS on mine now for some time and it works well.
No microG or Google Services, but F-Droid as appstore and if you have to install something which is only available on the Play store, there’s “Aurora Store” on F-Droid – Aurora is basically an alternative app for the Play store working with throwaway accounts.
Thanks for the advice. Although the phone wasn’t for me, the process of choosing one made me consider what I would consider buying if I had to pick up a new phone in the near future.
I think I would consider a Fairphone, though only refurbished ones are in stock in the online store. In the UK, where I could possibly buy a new one, the vendor (The Phone Co-op) only appears to offer them as part of a plan, which I’m not interested in. I’m sure that Fairphone would do a good job of refurbishing old phones.
The downside of buying used phones, especially old used phones, is the lack of support for newer versions of Android, so the experience gradually degrades over time as I discovered recently when various web services dropped support for certain versions of TLS. However, if an up-to-date version of LineageOS is available then I understand that this problem is solved to a certain extent - at least, as long as there is a maintainer for the model of phone you have.
I’m already using F-Droid on various Android devices. Thanks for the hints about Aurora. It’s not something I would use, but it’s good to know that it exists. 
And since there’s a new Fairphone out now, maybe this changes the landscape a little.
I can second the Fairphone (v2 at least). Used it for years, with their Fairphone Open OS branch. No difficult flashing: just select this OS variant, reboot and you have an Android install without the Google services. It still contains binaries for GPS and Bluetooth though. Best of all: it is supported by Fairphone.
I’m not sure what the story is for the new Fairphone 3, but I expect something similar.