I can't really rank games beyond Emerald, BW2, and ORAS being clear-cut favorites. So will just say my opinions on each. I also think you will get a vibe of what my favorite typings are in the games lol
Gen 1: Nostalgia sure and I love the Pokemon tower and Lavander Town themes, but overall buggy messes with godawful spritework to boot. Only Pokemon I truly love is the Gengar line and I guess Mewtwo. Blastoise is cool too I guess.
Gen 2: While I have a lot of nostalgia for them, I must say I find them overrated. they have unironically some of the best Pokemon spritework in the series, being way more dynamic and imposing than how Gen III does sprites. Also fighting Red is awesome. A lot of memorable tracks too. Beyond that? Not much of a fan of most Pokemon they add, progression in the game is very forgettable to me, and I just don't get why they are so beloved. Ho-Oh, Lugia, and the Dogs also don't particularly catch the eye for me. Standouts for me are Murkrow, Tyrannitar, Skarmory, Xatu, and Espeon/Umbreon
Gen 3: Favorite soundtrack, most tracks are still ingrained in my mind. Too many Pokemon designs to count that I love, lemme think: Sceptile, Gardevoir, Sharpedo, Claydol, Duscops, Metagross, Absol, Groudon, Rayquaza, and Deoxys are all awesome. I find the routes memorable with many interconnections and hidden areas. Secret bases. Fun postgame in Emerald (My favorite Pokemon game aside for maybe ORAS or BW2), introduced the hex maniac and her original design was still cute. Not much to say for FRLG just don't like Gen 1. Oh yeah has my favorite opening, I Wanna Be a Hero
Gen IV: Never got to enjoy them though I have a copy of Diamond (Aiming for Platinum). Can't say much on them beyond Pokemon I like: Spiritomb, Honchcrow, Froslass, Dusknoir, Palkia, Giratina, and of course Arceus. I used to like Darkrai but now hate him but that's for personal reasons nothing on Darkrai he's awesome.
Gen V: When they first came out I hate them as too many of the designs were just weird and off-putting and I wasn't a fan of the anime. I also thought the graphics looked ugly. Over the years my opinions have flipped. On an objective level, the only thing BW2 is missing is fairy type, otherwise this is peak Pokemon. The graphics are amazing, the absolute pinnacle for Pokemon with beautifully animated sprites and breathtaking setpieces. The most memorable and unique gyms in the series with their own unique soundtracks. Speaking of unique soundtracks, the music in these games are superb, some even becoming memes due to how memorable and catchy they are. As for Pokemon I like? Samurott, Beheeyem, Gothitelle, Chandellure, Sigilith, Golurk, Zekrom, and Kyurem. If not for nostalgia goggles making me love Emerald the most, I'd argue BW2 are objectively the best of the 2D games
Will do Gen VI-VIII later