I'm pretty fond of my OnePlus X - it's the first phone I've owned that has performance I'm happy to call “adequate”. It runs along nicely, no questions asked. It never really stutters or has a little moan at me. Battery life is a little weak for my use case, but that's fine. I'm almost always near electricity.
I do a lot of work in the Middle East, and before I go I like to clear out my phone, study what I use it for and return it to being a lean device. My standard target has been CyanogenMod, which I've been running since it started. That's no longer developed, so I need to take a little look at alternatives. The OPX mod scene is a little slow these days - the phone is discontinued and never had the biggest sales figures, so there isn't the most motivated talent pool to keep it up.
I'm settling on the direct descendent of CM, LineageOS. It's more or less the same developers and codebase under a different name. Currently available for the device (Codename: onyx) is 14.1, which translates to Android numbering as 7.1, or “the latest and greatest”. While there are driver deficiencies - I don't believe that Qualcomm are going to produce graphics drivers for the snapdragon 801 - people report it runs well.
I'm scaling back my google dependency a little more, this time I can get rid of music, photos, books, gmail, films, keep and a whole load of other stuff I don't care to remember. OpenGAPPS pico does me fine and I'll install what I need.
I listed the apps I actually use and care about, and it came to about 30:
Action3 Calendar? Drive Firefox F-Droid iPlayer Radio K9-Mail (fdroid) KDE-Connect (fdroid) Monzo Nextcloud (fdroid) Openkeychain (fdroid) (backup) Orbot (fdroid) Orfox (fdroid) Password Store (fdroid) Podcast Addict (backup) Plus Revolut RBS Riot Simple Last.fm Scrobbler (fdroid) Signal (backup) Spotify Termux (fdroid) Twitter VLC Weechat Android (fdroid) Whatsapp (backup) Youtube
Google Drive is required for whatsapp backups, but it has been uninstalled now that whatsapp is restored.
Openkeychain has really, really impressed me in my migration process - it let me export my phone gpg key (used for password store) securely, with a long password to protect it. I was able to move and import easily on the new OS.
Everything's been relatively painless, to be honest. Ownlcoud replaces google photos, and a whole load of other functions too. It brings ever more of my data back under my control, which is pretty important when you've got secrets to hide from nasty Governments like I do. I've got an increasing amount of free software there too - fdroid becomes ever more useful for me.
LineageOS is running smoothly. My only issue is that it would not let me write to my SD card from apps, so I couldn't download podcasts to it or cache spotify. It's a weird quirk that I'm sure will get worked out. Until then I've done the co-opted storage thing, which I really don't like.
Battery life is still crap, but I think it's slightly less crap than it was, time will tell!