Which Hard Disk is Best for creating super fast performance computer ?

I want to buy a new Hard Disk from online . For this I have seen various kinds of Hard Disk and it’s seems to me that all Hard Disk are good But I know all are not good. For this it’s very hard to choose perfect Hard Disk for me because I don’t know and understand anything about electronic product even in Hard Disk . But I want to buy a good Hard Disk . So I want help from the expert person. My questions is –

1. What should I see before buying a new Hard Disk ?
2. Which Hard Disk is Best for creating super fast performance computer ?

I will be very grateful to you if you help me to buy a good Hard Disk . Thanks to all