This is the 12795th most frequent Turkish word.
iyisinin
"The best of it" or "the better one."
The word "iyisinin" is used as a comparison to imply 'the better one' emphasizing the superiority of something in quality.
Bu konuda iyisinin siz olduğunu düşünüyorum.
I think you are the better one in this matter.
Here, "iyisinin" indicates the best choice or option among a category, indexed by high quality.
Kaliteli ürünlerden hep iyisinin peşindeyim.
I’m always after the best of high-quality products.
"iyisinin" identifies the superior choice among a collective group of items, suggesting significance or priority.