Anka is better at closing the kill quickly by the end of the game, and getting away, but you have to be skilled with her.
Taka is good by mid-game depending on how you build him, but he’s not as good at closing the kill meaning the enemy usually has to be weakened first for him to get a kill easily. He is better, however, at sustaining himself during teamfights, and getting surprise kills.
The basic difference is that if you’d rather play safe or aren’t as skilled, play Taka for the healing and stealth he has. If you’re willing to risk more and are good with your timing and positioning, play Anka for the sheer killing power she has on enemies, as well as her evasion abilities.
Also, Taka is better against burst heroes while Anka is better against damage-over-time heroes.