In my opinion the best in the counter strike series is Condition Zero. There is Counter Strike Source though. Most people say it is much better due to the Source engine. The Source engine has increased graphic quality etc. The reason you wouldn't get source is if your computer can't handle it well (as in low framerates, direct X, pixel shader, vertex shader, and etc.) I do not own Source myself, but I believe the game has the right to be called "The Best Version of Counter-Strike"