As of right now, I think mobile Linux still needs some more time before it's ready for mass adoption. For the developers and tinkerers, it's a fun project and, depending on your needs, it can be usable as a daily driver as your main or side phone, but it's still a little unstable with many missing conveniences compared to the duopoly. App support is already good enough in my opinion, especially with Waydroid being a thing. As for device support, I think if you do want to try mobile Linux, get a well-supported device to start, like a used OnePlus 6 or Pixel 3a series, and just play around with it. I found it very fun, and there are lots of cool things you can do with mobile Linux too! I particularly enjoyed the lack of microtransactions in all the games...(Animatch, Ultimate Tic Tac Toe, Pentobi, a few desktop games are playable with mouse and keyboard)
A good alternative right now is to recommend a degoogled Android ROM for people who want to keep the openness of Android but don't want to go all in to Linux phones just yet. iodeOS, GrapheneOS, e/OS, and now CalyxOS (they're back!) are all great options that won't have the same restrictions as stock Android. Fairphones, Pixels, etc. are all great devices to be recommended for this purpose.