My vote is for the 1901. Though the 1896 is 15 attack and the others are better IV, Entei has high HP, and will benefit more from Attack and Defense. Having good Defense on it will give it more longevity. The highest two are pretty impressive, but they prioritize HP, which Entei doesn't need quite as much.
Which Entei to power up? I live in an area where the weather is clear 80% of the time