|The base game is required before you can purchase anything else. Expansion packs, as the name suggests, are created to expand on the game, but not provide the game itself.|
The Sims 2 core game can be bought by itself as a regular game, or as included in one of the following games:
-The Sims 2 Special DVD edition: as stated, this comes with a special DVD
-The Sims 2 Holiday Edition (2005 Edition): Also known as the Christmas Party Pack, this comes with holiday themed items
-The Sims 2 Holiday Edition (2006 Edition): Comes with Happy Holiday Stuff. Overall, it's better than the 2005 edition in that it allows your Sims to throw get-togethers and wear different fashions
-The Sims 2 Deluxe: Comes with the Nightlife expansion
All of the above listed (including the base game BY ITSELF) are not being sold in stores anymore. The one currently in stock is called The Sims 2 Double Deluxe, which comes with the Nightlife expansion and a stuff pack, called Celebration stuff which, as its name suggests, is designed to enhance your game with upscale wedding/birthday/anniversary designs and objects.
I'd personally recommend Double Deluxe, but it's really up to you.
Hope I helped!
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