Is nesting better than the alternative?

This is more of a general question and opinion. I was wondering which would be better in terms of runtime speed, file size and security.

I saw recently a program where
instead of using Nested code.
Ex.

if(blank){ if(blank){ if(blank){ } } Run whatever code is needed... }

it would use this following format.
Ex.

if(!blank) { Return error; } if(!blank) {Return error; } if(!blank) {Return error; } Run block of code if all above are true.

What is the general opinion on this and which one is best in terms of speed, size and security.