Which one?

[Ric]

I have played all of these games through from beginning to end, even Pokémon Green which only came out in Japan.

Gold, Silver and Crystal are by far the best of the series and after playing them all (I haven't completed Crystal yet though). I believe that Crystal is the best one yet, it takes all the elements that made Gold and Silver good and improves upon them. There are also a number of new elements such as the battle tower and advanced storyline with Suicune. IMO: By far the best addition to the series yet.