Answer 1

Heartgold and soulsilver have a lot to.

Moltres,Zapdos,Articuno,Red Gyrados?,Raikou,Entei,Suicune,Lugia,Ho-oh,Kyogre,Groudon,Rayquaza,Celebi,Dialga,Palkia,Giratina,Latios,Latias,Jiachi.

Sooo yah thats 18 legendarys.. not counting red gyrados

Oh AND Mewtwo..

Source: http://pokemondb.net/pokebase/82692/which-pokemon-game-has-the-most-legendary-pokemon-on-it

Comments

I sont think you can get jirachi, dialga, palkia and giratina unless u get it from events

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You can also capture alot of Legendaries in pokemon Black/White 2

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Yeah you can get a lot of legendaries in BW2, but I compared the two games, and HGSS has one or two more legendary pokemon that you can get.

Answer 2

Heartgold and Soulsilver versions.

Look here if you want details on each legendary that you can find in HGSS

Source: I counted the legendary Pokemon