For me, it's Emerald. The best Pokemon Game. I even ask for extra Emerald cartridges and the staff is so friendly and more than willing to oblige.
One time I asked for Emerald cartridges and they gave me three. I said, "Wow, three for free!" and the nice friendly GAME worker laughed and said, "I'm going to call you 3-for-free!".
Now the staff greets me with "hey it's 3-for-free!" and ALWAYS give me three cartridges. It's such a fun and cool atmosphere at my local GAME store. What a great store.