I bolded the ones that are probably strongest.

Place smells:

-forest (he trains there almost daily)
-CH1
-plaza, particularly the rooftops
-less frequently, the mountains

Also worth noting, he staunchly avoids the battle dome. So. Never any smells there.

People smells:

-any of the Naruto ninja living in CH1
--one of these people, his sensei, is a chain smoker
-Masaomi Kida (his roommate)
-possibly Katara

Animal smells:

-a cat
-Masaomi's Pichu
-Kiba's dog, Akamaru
-DEER. He works with them frequently.

Activities:

-ninja training, weapons and explosives
-idk if this has a smell, but board games
-cloud watching (so grass and/or plaza rooftops, again)

Other:

-I'm-a-teenage-guy-this-shirt-still-smells-clean