PS1: Honestly don't remember...I think it might have been FF8, certainly my strongest early PS1 memory. Yes, not that early, but I got most of my consoles late as a kid up until PS3. And yeah, I played FF8 before 7 which is probably why I have a different opinion of both games than most people (love them both though).
PS2: Final Fantasy X. Playstations were over 60% my Squaresoft/RPG machines at the time. I really, really felt the difference in FFX and missed the world map (still do, and still don't think FF's ever been quite as good since), but it's a fantastic game and I loved it to bits. Shame most of the side quests are oddly bad especially after FF7-9 were such a treat. Actually it might have been Onimusha, again, don't have perfect memory here. I think I got them both.
PS3: Resistance. No surprise as it was the 1 good launch game and I did get it at launch. I actually did really, really enjoy the game and the series, no memes here.
PS4: Resogun. I also had Killzone Shadowfall but was most excited for Resogun, it's great. Got the plat (but not all the DLC trophies).