/vp/ VGC 2017 viability tiers

A+ (Pokemon that  dominate the meta, can run various sets/items making them unpredictable, most teams will use 2 or more of them)
Arcanine
Celesteela
Garchomp
Porygon2
Tapu Fini
Tapu Koko
Tapu Lele

A (Also strong in the meta but typically more constrained by move/item requirements and are more predictable than A+ tier threats)
Araquanid
Kartana
Krookodile
Muk-Alola
Tapu Bulu

B+ (Pokemon that are very useful in the meta, may counter A+/A threats or simply be threats that require more team support to function)
Gastrodon
Gigalith
Golduck
Mandibuzz
Marowak-Alola
Metagross
Nihilego
Pelipper
Salamence
Torkoal
Vikavolt

B (May counter higher tier threats, be used to patch up holes in team composition, or may be HIGHLY support dependent threats)
Drampa
Goodra
Gengar
Gyarados
Hariyama
Magnezone
Mimikyu
Milotic
Mudsdale
Nintales-Alola
Oranguru
Persian-Alola
Politoed
Porygon-Z
Pheromosa
Xurkitree

C+ (Have some applications in the meta, but face poor matchups against or competition from higher tier pokes for a team/item sot)
Aerodactyl
Mismagius
Raichu-Alola
Snorlax

C (Have a unique niche, but typically either don't offer enough utility for the slot or need more support than they are worth giving)
Braviary
Kommo-o
Primarina
Sandslash-Alola
Silvally
Talonflame
Togedemaru
Vanilluxe
Whimsicott

D (Generally very inflexible and not outstanding even in ideal conditions, but may be surprising to unprepared opponents)
Bewear
Buzzwole
Comfey
Clefairy
Dugtrio-Alola
Eevee
Exeggutor-Alola
Incineroar
Liligant
Parasect
Poliwrath
Smeargle
Stoutland

Unlisted (Pokemon that don't really have a place in the meta right now)
Everything else. Some good/decent pokemon in past formats have been rendered basically useless by changes in the pace of the meta (Weavile, Lucario), losing tutor moves (Scizor, Weavile), facing competition from new pokemon or pokemon not viable in previous metas (Scizor, Trevenant).