choosy
Very picky and hard to please about choices.
Someone who is choosy is very particular about their choices and not easily satisfied. A choosy eater might refuse perfectly good food because the cheese isn't melted just right, or because their sandwich bread has sesame seeds instead of being plain. A choosy reader might reject book after book at the library, looking for exactly the right story.
Being choosy means having high standards and strong preferences. When your friend is choosy about who she sits with at lunch, she cares a lot about finding the right companion. When a college is choosy about which students it admits, it's being selective and careful.
There's a balance to strike here. Being somewhat choosy can be helpful: a choosy scientist carefully evaluates evidence before drawing conclusions, and a choosy coach selects the best players for important positions. But being too choosy can cause problems. If someone is so choosy about a birthday present that nothing seems good enough, they might end up disappointed.
The word often carries a slightly negative tone, suggesting someone is being unnecessarily picky or hard to please.