Side by side
Search types
AKC uses container, interior, exterior, and buried searches. NACSW uses container, interior, exterior, and vehicle searches. Vehicle work is more central to NACSW. Buried work is part of AKC.
Odors
Both start with birch and add anise and clove at higher levels. Some sources also mention cypress or other oils for certain classes. Confirm in each rulebook.
Levels
AKC levels run from Novice up through Advanced, Excellent, and Master, with Detective at the top. NACSW levels run from NW1 through NW3 and then Elite and beyond.
How titles work
AKC usually awards titles per element and level, through repeated qualifying scores. NACSW awards its entry level titles by passing the whole day, with its own rules for higher levels. The exact numbers are in the rulebook and change over time.
Odor test
NACSW requires an Odor Recognition Test before a dog may enter a trial. AKC works differently. Check AKC's current steps.
Notice that most of these differences are about rules and logistics, not about what your dog will feel while searching. A dog does not know which logo is on the paperwork. They know whether the game is fun and whether you are calm.
Also note that both organizations update their programs. New levels, new odors, and new rules appear over time. If you read an old blog post or hear a tip from a friend, check it against the current rulebook before you rely on it.