Even more important than just playig with "curved" or "straight" fingers is the way how you move your fingers.
It has been thoroughlly researched that the most efficient way of playing is the way, were fingers move sensitively. It means, that all three parts of every finger are in motion and are involved in the playing process.
So the finger pushes the key down while going from curved position into more straight position.
So can each finger be really independent. And the soft pads can make a very good contact with the instrument. You should not play with nails
Also very important is the knuckle support.
Basically, every time you want to see the most natural hand position, stand up and let your hands fall 100% loose.
Then you will see - the fingers are curved, knuckles can be seen the wrist is in the normal position. And that is the position where teachers always try to push their students.
So just stand up with loose hands and you will see it.
P.S. all the explanations here are very brief of course.