Sand levels better if you want to get to a point where your lawn is like a golf course, but it adds some other complications and some more work. Long story short, sand levels better, but probably use screened topsoil until your soil is where you want it to be from a nutrient perspective. I've been hesitant to use sand yet, but might at some point.

https://www.youtube.com/watch?v=JImcRT7x-8M