There are two types of loads that a fastener can provide:

- shear 

- pullout

Screws obviously would do better in good, dense wood on pullout strength. 

Some versions of nails (a common 16d nail), manually driven home) will have a higher shear strength than a #10 screw. A nailgun nail might be on par with a #10 screw. 

Screw pullout or tensile strength depends on the thread form, but is usually much better than common nails.