Nn, it depends. Usually you want to stare at the whole screen for usual gameplay. I'd tell you to practice both, because looking at each note individually with your eyes, although it's hard, it makes your osu! life easier later on.
TL;DR: Do both. Look at each note individually for screen side-to-side jumps. Ex: Remote Control [Insane]'s jumps (although it's the hardest insane I've ever seen on my whole life)
TL;DR: Do both. Look at each note individually for screen side-to-side jumps. Ex: Remote Control [Insane]'s jumps (although it's the hardest insane I've ever seen on my whole life)