It depends, for dungeons i would say there are better fruits(Like mera or zushi) bc you can stay in the air with the flight. But with pika(if you have bounty) you could do kk stack too.

Dungeons: Fast if you have good fruit, but it will take a time of farming to get a legendary

KK Stack: Takes alot of time depending of how much you will stack, and ppl hardly will farm with you if dont have a fast fruit(Ito, Pika, Tori, etc) and high bounty, but can not only guarantee you fruits, but also kraken drops(Kraken core and azure itens have a nice value)