Best Wishes featured almost no all pokemon at all through this series. Best Wishes 2 start featuring older pokemon frequently. Although for the anime aren't strictly debuts, for Best Wishes it is. And because almost all Unova pokemon has already debuted (save a couple of them in the League) I do a list of older pokemon.
The list of Pokemon that already debuted in Best Wishes are: (not left to debut because is so long)
(BWS1 01) Pikachu, Meowth, Persian
(BWS1 04) Umbreon (pokedex)
(BWS1 56) (only in photos). Spheal, Sealeo, Tauros, Shinx, Luxray, Combee, Bidoof, Staravia, Lickilicky, Cherubi, Skorupi.
(BWS1 84) (in the form of mecha-Tyranitar) Tyranitar
(BWS1 85) Koffing
(BWS2 01) Piplup, Garchomp, Glaceon
(BWS2 02) Buneary, Pachirisu, Mamoswine, Quilava, Togekiss, Staryu, Wailord, Wingull, Rattata.
(BWS2 03) Onix, Krabby, Kingler, Remoraid, Magnemite.
(BWS2 04) Larvitar
(BWS2 05) Dragonite, Magmortar
(BWS2 09) Riolu, Milotic (dream)
(BWS2 10) Mantine
(BWS2 12) Rhydon, Golem
(BWS2 14) Roserade
(BWS2 15) Corphish, Buizel
Confirmed to debut: Altaria (BWS2 17), Eevee, Vaporeon, Jolteon, Flareon, Espeon, Umbreon* (physically), Leafeon (BWS2 18), Lucario (BWS2 ??), Charizard (in some episode, appears in merchandise very heavily)
Pokemon debuted: 32/493. If count photos and mechas: 45/493. If you count photos but not mechas 44/493.