The second G3 Cheerilee, and the older G3 pony Cherry Blossom. G’wan, you tell me which is which. When Core 7 Cheerilee came along, a lot of people wondered why they turned Cheerilee, who was previously the leader of Unicornia, and still purple but in quite different shades, into a clone of Cherry Blossom instead of just using the actual Cherry Blossom.
 
Of course, the FIM comics have them as twin sisters. Double the homage value - nod to the earth pony Cheerilee being a Cherry Blossom clone and now G4 Cheerilee has an athletic sister like her G3 counterpart.
 
There are small difference aside from the cutie mark that can be noticed when you put them side by side: the hair, purple/pink/light pink vs. purple/pink/white; the eyes, three shades of green vs. one; and Cherry Blossom is actually a bit darker. (As for the difference in hair, blame some kid’s scissors.)
 
Edit: Uh, that’s Cheerilee on the left and Cherry Blossom on the right.