OpenWrt is what I use. I picked my routers specifically to be well supported by OpenWrt, immediately wiped whatever the original firmware and installed OpenWrt and that was about ten years ago. Then when I replaced the hardware I also looked for a compatible model with OpenWrt and did the same.
I never had any issue with OpenWrt which I couldn't solve and it just works. Its uptime is pretty much the uptime since when the power goes out due to storms and such.
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