Faker only uses Smartcast.

Is quick cast better LoL?

Using quick cast can be invaluable because it reduces the time delay between activating and casting by cutting the user input in half; activate vs activate and click. Remember that quick casting means you don't get the targeting graphic, which can make it harder to accurately aim skillshots.

Should I use quick cast or normal cast?

With quick cast it totally eliminates the step of the range/targeting graphic and just casts the ability instantly based on where your mouse is. The advantage being less time spent on targeting your ability, which would mean a faster reaction and skill shot use. + Cuts down ability usage time by a significant amount.