FAVORITES

Neither the regional Pokémon here nor any of their evolutionary stages are in any of the listed parties, unless I prefer a specific evolutionary stage over the Pokémon in the listed party. And, generally, I like most of these Pokémon for their aesthetics; or that I trained one of them for fun at some point and got attached.
Any of the Sceptile evolutionary stages can be assumed to also be in any of the form categories, if applicable.
Hover over the categories to see unlisted favorites (in teams.)
The avatar to the left is my favorite NPC trainer design.

World

Region Hoenn
Story Playthrough Gen 5 (Black/White)
Game Omega Ruby, Heart Gold
Type
Team Team Magma Team Skull

Humans

Trainer Yellow, from Pokémon Special (Favorite Overall Trainer) Gold/Ethan, from Johto (Favorite Male Trainer) White/Hilda, from Unova (Favorite Female Trainer)
Rival Not listed (minor favorites): Brendan/May, Wally, Bianca, Gladion N, from Unova (Favorite Overall Rival) Green, from Kanto Emma, from Kalos
Gym Leader Not listed (minor favorites): Sabrina, Jasmine, Clair, Flannery, Winona, Tate & Liza, Wallace, Maylene, Candice, Elesa, Skyla, Drayden, Cheren, Marlon, Ilima, Lana, Mina Roxanne, from Rustboro City in Hoenn (Favorite Overall & in Hoenn) Erika, from Celadon City in Kanto (Favorite Kanto) Falkner, from Violet City in Johto (Favorite Johto) Volkner, from Sunyshore City in Sinnoh (Favorite Sinnoh) Cress, from Striaton City in Unova (Favorite Unova) Olivia, from Akala Island in Alola (Favorite Alola)
Elite Four Caitlin, from Unova (Favorite Overall) Phoebe, from Hoenn Grimsley, from Unova Acerola, from Alola
Champion Steven Stone, from Hoenn (Favorite Overall) Cynthia, from Sinnoh Iris, from Unova
Battle Boss Pike Queen Lucy, in the Battle Pike (Hoenn) Battle Chatelaine Morgan, in the Battle Maison
Team Admins Shelly, from Team Aqua (Hoenn) (Favorite Overall) Colress, from Team Plasma (Unova) Malva, from Team Flare (Kalos)

Categorized

Eeveelution Umbreon
Vivillon Pattern Ocean Pattern
Nectar Style Pom-Pom
Seasonal Forme Winter Forme Winter Forme
Flower Color Red (original) Red (original) Red (original)
Legendary Kyurem (Overall Favorite Legendary) Latios Giratina
Trios Articuno (Legendary Birds) Suicune (Legendary Beasts) Regice (Legendary Titan) Mesprit (Lake Guardian) Virizion (Swords of Justice)

Regional

Kanto Not listed (in teams): Ponyta/Rapidash, Pidgeot, Arcanine Bulbasaur Jigglypuff Diglett Cloyster Ditto Dragonair
Johto Not listed (in teams): Kingdra, Chikorita line, Furret, Marill line, Aipom line Cyndaquil Ampharos Slowking Phanpy
Hoenn Not listed (in teams): Treecko line, Aron line, Blaziken, Poochyena line, Taillow Pelipper Masquerain Mawile Manectric Flygon Altaria Zangoose Milotic Tropius
Sinnoh Not listed (in teams): Luxray Roserade Drifloon Buneary Lickilicky
Unova Not listed (in teams): Bisharp, Mienshao Scolipede Whimsicott Darumaka Braviary Deino Hydreigon
Kalos Not listed (in teams): Talonflame, Amaura line, Florges, Aegislash, Gogoat Pancham Slurpuff Goomy
Alola Not listed (in teams): Alolan Ninetales, Lycanroc, Stufful line Rowlet Salazzle Comfey Mimikyu Dhelmise

Forms

Alolan Forms Alolan Raichu Alolan Sandshrew Alolan Vulpix Alolan Dugtrio Alolan Golem Alolan Muk Alolan Exeggutor Alolan Marowak
Mega Evolutions Mega Charizard X Mega Gengar Mega Kangaskhan Mega Aerodactyl Mega Gardevoir Mega Sableye Mega Glalie Mega Salamence Mega Gallade
Shiny Charizard Ponyta Alolan Muk Mega Gengar Alolan Marowak Aipom Umbreon Ralts Electrike Mega Camerupt Zangoose Glalie Metagross Primal Groudon Mothim Buneary Mega Gallade Emboar Musharna Whimsicott Zorua Chandelure Furfrou Sylveon Xerneas Primarina Midnight Lycanroc

OTPs

Red/Gold (Poli[HeartGold]shipping) Black/White (Chess[Agency]Shipping) Diamond[Lucas]/Platinum[Dawn]/Pearl[Barry] (Entourage[Scarf]Shipping) Steven/Wallace (OriginShipping)
Lisia/May (ContestQueenShipping) Cheren/Bianca (DualRivalShipping) Shauna/Serena (BoutiqueShipping) Gladion/Hau (CutebonesShipping)
Moon/Lillie (OceanflowerShipping) Sapphire (May)/Leaf (Blue) (ScientificShipping) Cynthia/Caitlin (AccessoryShipping) Blanche/Candela (MollifyShipping)

Ships

Red/Green (Original[Begins][Nameless]Shipping) Red/Green/Leaf[Blue] (HistoryShipping) Ariana/Archer (ClonegeuseShipping) Silver/Gold (PreciousMetal[Hunter]Shipping)
Gold/Silver/Crystal [Pokémon Adventures specifically] (JohtoShipping) Morty/Eusine (SacredShipping) Ruby (Brendan)/Sapphire (May) (Hoenn[Frantic]Shipping) Steven/Brawly (StrengthShipping)
Mr. Briney/Mr. Stone Archie/Maxie (HardenShipping) Courtney/Shelly (AlphaFemaleShipping) Tabitha/Matt (GaslightShipping)
Flint/Volkner (IgnitionShipping) Black/White/N (MonochromeShipping) Professor Juniper/Professor Fennel (ScientificShipping) Hugh/Nate (GreySkyShipping)
Green/Silver (Secondary[Bruise]Shipping) Yellow/Iris (PaintedDragonShipping) Bebe/Lanette (WANshipping) Steven/Cynthia
James/Jessie (RocketShipping) May/Zinnia (AlphaIdealsShipping) Ilima/Kiawe (YellowFlowerShipping) Kukui/Burnet (EternalHoneymoonShipping)
Kukui/Burnet/Olivia Mina/Mallow (CrushedberryShipping) Acerola/Lana (MysticBubbleShipping) Lusamine/Wicke (HeavenlyShipping)
Cynthia/Diantha (PhaesporiaShipping) Nanu/Looker (PoliceShipping) Accelgor/Escavalier (IWantMyHelmetBackShipping) Ash's Pikachu/Team Rocket's Meowth (Kat&MouseShipping)