When I look at the current number I can easily predict that the Wii franchise will be at least in the top 3 sometime soon.
1. Mario - 302M
2. Pokemon - 152M
3. Grand Theft Auto - 61,5M
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15. Wii series - 26,35M
They are only 2 franchise that have sales over 100 millions and GTA as only 61 millions sales. At the Wii current rate of sale, they will surely pass the 61 millions of GTA even if the new GTA IV sells a lot. This will make the top 3 of best franchise all Nintendo series.