None of them, Counter Strike: Condition Zero is the closest to Counter Strike 1.6...
Counter Strike: Condition Zero is based on the gold source engine, and so do Counter Strike 1.6 so there is a possibility that you can play with him trough Counter Strike: Condition Zero, anyway, you cant play with him trough Counter Strike: Source because it uses the 'normal' source engine...
You can download Counter Strike 1.6 hacked from the Internet, just search in google...
(The difference between source and gold-source is:
Gold-source - Uses Half-Life 11 to run.
Source - Uses Half-Life 2 to run.)
Oh, and i noticed something weird, you cant play multiplayer from cracked to real, so ask you're Friend if he has cracked first :D
Hope i helped :D