XY(Z) > DP > AG > SM (So Far) >= OG = BW
Original Series
Plot: 6 (TR as a whole could've done more, and there could've been less filler, especially in Johto. Kanto is fine but Johto & OI...Johto League was cool, as was the Team Rocket/Lugia storyline, Ash/Gary's rivalry with hindsight wasn't that great since it was mostly Gary doing a lot trash talking without giving Ash a chance to prove him wrong and them only battling TWICE is 270+ episode series)
Characters: 7 (Brock and Misty were fine in Kanto, but in Johto they were staler than a year old bag of potato chips. Tracey was always cardboard).
Group Chemistry: 8 (Ash/Brock/Misty still have some of the best chemistry, however I can't say the same for Ash/TRACEY/Misty)
Ash Himself: 6 (I'm not too fond of pity badges, but I do like that he improved come Johto)
Overall: 6.5
Advanced Series
Plot: 7 (Team Aqua/Magma could've been more involved, but the adventure in Hoenn & Battle Frontier and May's Contest were fun)
Characters: 7.5 (May is my 2nd favorite girl and a big step up from Misty, I don't care for Max, and Brock is still a piece of furniture)
Group Chemistry: 7.5 (A step down from the OG group. Brock felt like he was friends with May and Max because they were friends with Ash at times).
Ash Himself: 7.5 (He's taking the initiative to train more, caught a good team, mature enough to mentor May, uses his head more, and retains some childishness)
Overall: 7.5
Diamond & Pearl
Plot: 8.5 (Team Galactic is probably the best organization, J is my favorite villain, a darker plot with Ash's best rival to date. Dawn's contest were fun as well)
Characters: 7 (I can see why Dawn's a fan-favorite, but she's in 3rd place for me. Brock is practically wallpaper at this point...)
Group Chemistry: 6 (Ash/Brock = Brothers, Ash/Dawn = Twin Siblings, Brock/Dawn = Associates through Ash)
Ash Himself: 8.5 (Mature/Competent/No longer a kid Brock is babysitting, learns from his mistakes and dwells on them to improve, had the tuition to use his older pokemon even if the most blatant case of Dues Ex Machina the anime has ever conceived stopped him from winning the Leauge, and had some childishness in him)
Overall: 8
Best Wishes
Plot: 6.5 (Team Plasma and Rocket were fine, pacing reminds me of Kanto a bit, although the 4-6 months of filler to stall for time for XY really hurt this series. I don't think it's as bad as some say it is.)
Characters: 6 (I like Iris and Cilan to an extent, they have personality but not much else. I like them better than Post-Kanto Brock & Misty)
Group Chemistry: 7 (A diet version of Ash/Brock/Misty if you will)
Ash Himself: 6 (How do you downgrade from Mature/Competent to immature/idiot? In Kanto you had the beginner excuse but now?)
Overall: 6.5
XY(Z)
Plot: 9 (Most fun I've ever had watching Pokémon, Badge Quest was great, I enjoyed Serena's TriPokalons, Sawyer and Alain are two of my favorite rivals of Ash, Team Flare is equally as good as Team Galactic and the climax is the best yet, I really enjoyed the Ash/Serena romance subplot. Out of 140 episodes, only TWELVE I thought were bad and that doesn't even equate to 10% of this series).
Characters: 9 (Imo Serena is the most human/developed female lead to date. Clemont is the most developed male companion of Ash, and Bonnie was Max done well and in my Top 5 of our 9 female leads. I thought everyone had a nice share of development, I enjoyed their episodes, and think collectively these are Ash's best companions.
Group Chemistry: 9 (Imo they closest knit group of the series whether it was a heavily focused pair: Ash/Serena, Clemont/Bonnie or a least focused one Ash/Bonnie, Serena/Clemont I enjoyed seeing these four interact. I felt like even though Ash/Serena were the stars, they all did feel like equals with everyone being important to the group/plot, and everyone having their time to reflect on how much they've grown instead of just Ash).
Ash Himself: 9 (Ash is again mature/competent, learns/dwells on his mistakes to improve, he's a leader this time around and gave SOME clarification on what a "Pokémon Master" is and felt the closest he's ever gotten to achieving that goal. Caught the best regional team yet, and got the farthest he's ever gotten in the league, and acts like he has five regions of experience on the battlefield and off of it despite still having a little childlike naivety in him).
Overall: 9
Sun & Moon Series
Plot: 6.5 (I'm not feeling the slice of life approach this series is taking. The school is practically a setting rather than something important like it was advertised, the adventure aspect isn't really present since Ash is stationed on Melemele Island 85-90% of the time and whenever he does leave said island he comes back after a few episodes, and while I enjoyed some of the Aether Arc. it felt really rushed).
Characters: 6.5 (I'll get to them)
Group Chemistry: 6.5-7 (Aside from Lillie/Mallow, Ash/Kiawe, Ash/Kukui, and MAYBE Ash/Lillie, I'm not feeling this group)
Ash Himself: 6.5 (He has his DP/XY Competence on the battlefield and SOMETIMES off of it, but it's like BW Ash all over again at times. WTF happened to you?)
Overall: 6.7
Characters: They have potential, but due to the LARGE AND INCREASING cast, it's obvious that passable growth/development will be SPARSE amongst this group and so far it really shows.
Lillie: While I enjoy her episodes, they're as formulaic as the anime itself and the recent Aether Arc. really hyper focused on her and just gave her a lot of development on a silver patter aiding to the rushed feeling of the Aether Arc. and felt unearned almost. One minute she's afraid to touch pokemon, she's slowly overcoming this, gets reset and has a relaspse, remembers what happened and now she's glomping on EVERYONE'S Pokémon.....that kind came pretty fast...
Kiawe: I like him, he's the least amount of development episodes (or ties with Mallow), but I've enjoyed them. He has a hot blooded personality which is fun to watch, but he suffers from lack of focus due to SM's large cast
Lana: She has potential thanks to the Akala Island Arc. giving her a Z-Ring, before this I thought she was the least interesting female lead, but like Kiawe, a lack of focus due to the large cast of SM...and she has the largest number of focus episodes behind Lillie...
Sophocles: Essentially a fatter version of Clemont, but nowhere near as cool, developed, or focused and Clemont by this point in XY had a good number of focus episodes and development. What makes this worse for Sophocles is that he has equally as many focus episodes of Lana (or just one less).
Mallow: Eye candy with equally as many episodes as Kiawe, but hers are substantially less interesting. Next to Sophocles she's been shafted the most. All she has is a likeable personality and the role of being "Team Mom" that tries to keep everyone together that's it.