As of Omega Ruby and Alpha Sapphire, which game has the most Legendary Pokemon we can catch?

Question

Not counting psuedo-legendaries or Event Pokemon.

Answer 1

I'm going to answer this for both games in a series when applicable, since both have the same in either "half". Deoxys, while an event in most games, is not in ORAS.

Omega Ruby and Alpha Sapphire: 32 Legendaries
X and Y: 6 Legendaries
Black 2 and White 2: 17 Legendaries
Black and White: 9 Legendaries
Platinum: 12 Legendaries (the Regi trio were events)
Diamond and Pearl: 9 Legendaries
HeartGold and SoulSilver: 14 Legendaries
Emerald: 9 Legendaries (not sure if Mew is an event or not)
Ruby and Sapphire: 7 Legendaries
FireRed and LeafGreen: 9 Legendaries
Crystal: 5 Legendaries
Gold and Silver: 5 Legendaries
Yellow: 4 Legendaries
Red and Blue: 4 Legendaries

Omega Ruby / Alpha Sapphire has the most Legendary Pokémon by far, resting at a comfortable 32.

Answer 2

This may take a bit of time, but I'll try to get it done ASAP.

Pokemon Red & Blue:
4 Legendary Pokemon:
Mewtwo
Articuno
Zapdos
Moltres
Source

Pokemon Gold & Silver:
5 Legendary Pokemon:
Lugia
Ho-Oh
Raikou
Entei
Suicune
Source

Pokemon Crystal:
5 Legendary Pokemon:
Lugia
Ho-Oh
Raikou
Entei
Suicune
Source

Pokemon Ruby & Sapphire:
6 Legendary Pokemon (8 between both versions):
Kyogre (Sapphire excluisve)
Groudon (Ruby exclusive)
Regirock
Regice
Registeel
Rayquaza
Latios (Ruby exclusive)
Latias (Sapphire exclusive)
Source

Pokemon Fire Red & Leaf Green:
7 Legendary Pokemon (9 altogether)
Mewtwo
Articuno
Zapdos
Moltres
Raikou (If you chose Squirtle)
Entei (If you chose Bulbasaur)
Suicune (If you chose Charmander)
Source

Pokemon Emerald:
8 Legendary Pokemon:
Regirock
Regice
Registeel
Kyogre
Groudon
Rayquaza
Latios
Latias
Source

Pokemon Diamond & Pearl Legendary Pokemon:
8 Legendary Pokemon (9 between both versions):
Dialga (Diamond exclusive)
Palkia (Pearl exclusive)
Uxie
Mesprit
Azelf
Heatran
Regigigas
Giratina
Cresselia
Source

Pokemon Platinum:
15 Legendary Pokemon:
Giratina
Regice
Regirock
Registeel
Articuno
Zapdos
Moltres
Dailga
Palkia
Regigigas
Heatran
Cressellia
Uxie
Mesprit
Azelf
Source

Pokemon HeartGold & SoulSilver:
12 Legendary Pokemon (14 between both versions):
Latias (HG exclusive)
Latios (SS exclusive)
Ho-Oh
Lugia
Rakiou
Entei
Suicune
Kyogre (HG exclusive)
Groudon (SS exclusive)
Rayquaza
Mewtwo
Articuno
Zapdos
Moltres
Source

Pokemon Black & White:
7 Legendary Pokemon (9 between both versions):
Reshiram (Black exclusive)
Zekrom (White exclusive)
Cobalion
Terrakion
Virizion
Landorus
Kyurem
Tornadus (Black Exclusive)
Thundurus (White Exclusive)
Source

Pokemon Black2 & White 2:
15 Legendary Pokemon (17 between both versions):
Cobalion
Virizion
Terrakion
Zekrom
Reshiram
Kyruem
Latios (B2 exclusive)
Latias (W2 exclusive)
Uxie
Azelf
Mesprit
Regirock
Registeel (B2 exclusive)
Regice (W2 exclusive)
Regigigas
Cresselia
Heatran
Source

Pokemon X & Y
4 Legendary Pokemon (5 between both versions) (7 altogether):
Yveltal (Y exclusive)
Xerneas (X exculsive)
Zygarde
Mewtwo
Articuno (If you chose Chespin)
Zapdos (If you chose Fennekin)
Moltres (If you chose Froakie)
Source

Pokemon Omega ruby & Alpha Sapphire:
26 Legendary Pokemon (32 between both versions)
Kyogre (AS exclusive)
Groudon (OR exclusive)
Regirock
Regice
Registeel
Latias (AS exclusive)
Latios (OR exclusive)
Rayquaza
Deoxys
Lugia (AS exclusive)
Ho-Oh (OR exclusive)
Regigigas
Uxie
Mesprit
Azelf
Palkia (OR exclusive)
Dailga (AS exclusive)
Heatran
Giratina
Virizion
Terrakion
Cobalion
Resiriam (OR exclusive)
Zekrom (AS exclusive)
Kyruem
Raikou
Entei
Suicune
Thundrus (AS exclusive)
Tornadus (OR exclusive)
Landorus
Cresselia
Soucre

So! Here we are at the final scores! (Between both versions, including "Altogether.")
1st place: OR & AS with 32!
2nd place: B2 & W2 with 17!
3rd place: Platinum with 15!
4th place: HG & SS with 14!
5th place: D/P, B/W & FR/LG with 9!
6th place: R/S & Emerald with 8!
7th place: X/Y with 7!
8th place: G/S & Crystal with 5!
9th place: Red & Blue with 4!

Soooooooooo...
OR and AS win!

Hope this helps!