I'm hoping that my recently-purchased used Galaxy S5 will be good for the next 5+ years. Seriously.
Retina-level screen. Good enough horsepower for everything that I would need a *phone* to do. WATERPROOF. I can always add more storage. And I can just replace the battery when the old one gets worn. If it had 4GB of RAM instead of 2GB it would be even more of a tank.
My old S4 was really setting a longevity record until water got the best of it and messed up the GPS.
My Nexus (Samsung) before that just got too slow.
Run a custom rom and you should be butter for a long time.