While I am a diehard fan of modern Casio electric pianos, I got my start on a brand new Yamaha electric piano my dad kept in the basement. I would go down there as a kinder ~1990 and mess around on it, not understanding the patterns. The keyboard is HEAVY and built like a tank. Every component still works 33 years later. I'm not the biggest fan of the built-in sounds, but then we attached an aftermarket external midi-box that had better piano sounds. Today I'm keyboard proficient, with a bachelor's in music and a teaching career. Funny how it never would have happened, had my father not randomly purchased that old Yamaha which I never even heard him play or mess around with once. Unfortunately the Yamaha electric pianos I have tested throughout 2000-2016 (probably low and mid-tier in stores) could not match Casio in terms of build quality, including action, price-point, and in piano patches being close to "real" sounding.
Yamaha has made many p-series ("portable") keyboards over the years, and it's pretty confusing. I play a p-85 at home, which I'm unreasonably fond of, but when I travel I'm often playing other people's keyboards. When someone says they have a p-NNN available what does that mean?
Within the p-series there have been tiers, and within each tier Yamaha had many years when they'd make new versions that were very minor changes. Currently, the p-series tiers are:
Higher tiers cost more, but generally give you more or better features: physical response ("action") closer to a real piano, more voices, more pedals, more realistic voices, better interface for choosing voices, more simultaneous notes (polyphony) etc. Here's my attempt to make sense of the historical lineup. I've marked them with their release year, and in cases where they have a fancier action than GHS I've marked that as well.
Go back to the 90s and there's also the p-100, p-150, p-200, p-300, and p-500, which are all old enough that it's harder to get information on them, and you're much less likely to run into them.
Personally I'm happy with any of these; the features distinguishing the fancier models aren't ones I need. I like the built-in piano sounds (Piano 2 and Electric Piano 2 on my p-85) and at least from the p-70 onwards, use external midi for other voices, don't use the pedals, don't need more polyphony than I have fingers, use external midi for most voices, can handle either USB or 5-pin MIDI, and I like how light the GHS action is.