Had to screenshot this since the website wouldn't let me save it for some reason but here we are.
I didn't necessarily keep the releases together and they are mainly skewed to the ones I actually played.
Also this is a lot longer than I expected it would be (that's what she said) so, I guess sorry about the length.
S Rank
Red and Yellow - Red was the first game I played, borrowing my friend's copy and Game Boy Color in elementary school to get my first taste of mons. Not long after, Christmas came and I got Yellow while my brother got Blue. Seeing Pikachu follow me around and exploring Kanto was the most fun my young gaming self had had outside of playing Crash Bandicoot. These games set the foundation for my love of mons that still lingers all these years later and they are just classic. I won't turn down an opportunity to play these games. Myself, my brother, and cousins used to do speed runs on road trips to see who could get the most badges in a certain amount time. Lots of fun memories here.
Soul Silver - After playing RBY and GS upon their releases, I stopped playing mons for several years. Not sure why exactly, I had a Game Boy Advanced but just never got RSE or any of the new games for a long time. Then, I'm in college and my roommate whips out his DS and I see Soul Silver in his game collection and had never heard of it. He lets me explore his save file and it didn't take long for me to convince him to give it to me so I could start fresh. Seeing Kanto and Johto re-imagined was incredible to me (I didn't know that FRLG was a thing yet). Next thing I know I'm ordering a used DS online and I've been sucked into the world of mons again ever since. (I later gifted him a copy of Heart Gold as a thanks).
A Rank
Blue - I didn't play Blue since it was my brother's game, but I know how good it is since I loved Red and Yellow.
Silver - I enjoyed this game almost as much as Yellow. It really helped because my brother and cousin were still into mons too and we played our campaigns side by side. I was completely surprised that we got to explore an entire extra region after beating the game and thought that was really awesome. Beating the Elite Four, twice, and grinding to finally defeat Red was challenging and really fun. I can't think of moments in other mons games that compare to these.
Sword - Maybe its still fresh, but I enjoy playing this game a lot. I've put a lot of time into it and really like the Wild Area and what some of the gameplay changes could mean for the franchise, even though other aspects of the game and what came with it leave much to be desired.
Ultra Sun and Ultra Moon - For a while, until I caved and bought a Switch, I thought these would be the last mons games I played. With this in mind, I played them a ton and really enjoyed them even though the changes from Sun and Moon were slight. I enjoyed riding on Dusk Mane's back in search for rare mons and even found my first wild shiny (a Sigilyph) that wasn't a Red Gyarados. I also really liked the Battle Tree and was bummed to see a step back in battle facilities in Sword.
B Rank
Gold - I didn't play
Blue Gold since it was my brother's game, but I know how good it is since I loved
Red and Yellow Silver. I also thought Lugia was cooler than Ho-Oh but I was young and dumb so don't @ me.
Heart Gold - echo comments from Soul Silver but lower because of the old Lugia > Ho-Oh thing.
Fire Red and Leaf Green - I ended up playing these long after they came out since I kinda skipped the ADV era of mons initially. It was fun to see Kanto revamped and more colorful and all that. The nostalgia factor plays a big role here but they definitely aren't the best mons games around.
Emerald - Another game I played long after its initial release. I wanted to see what I'd missed out on so I ordered what turned out to be a bootleg copy of Emerald. It was fun, but I don't think I got into it as much as I should have because I don't think I even made it to the Battle Frontier, which I've heard a lot about.
X and Y - I played these shortly after getting back into mons via Soul Silver. Another instance of where a friend kindly lent me their copy and let me start a new save file, which is something I can't see myself doing easily. Mega Evolution was cool and the new graphics were fun to experience and I overall enjoyed playing these games but won't be rushing back to play through them again.
Sun and Moon - Fun games, slightly less fun than the Ultra versions though. I liked the region and the new mons.
C Rank
(Alpha) Sapphire and (Omega) Ruby - I really only played Alpha Sapphire and I thought it was a playable, fun installment but mainly enjoyed it for the new Megas. The mons overall in this gen are cool though. Flying on Lati@s was neat.
Platinum - My least played generation of mons outside of Gen 5, which I have not played basically at all. My first and only play through was enjoyable but highly forgettable. Empoleon is cool though.
Shield - Probably just as fun as Sword but you have to get Zamazenta and his movepool is garbage and utility in max raids compared to Zacian's is so sad.
D Rank
Diamond and Pearl - Echo comments of Platinum.
Haven't Played
Black (2) and White (2) - Some of you younger folk might be shocked to see I haven't played this gen, but I actually tried to at least. I was gifted a used copy of White and played maybe until I got one badge, but my house got robbed and my DS along with all my old games were stolen from me. Maybe one day I'll try to play these again.