Best way to check if a user is watching a space?

Hey there,
I would like to find out which spaces a user is watching.
I’m using the confluence server SDK.

So far I see two options, iterating all spaces and call
a) NotificationManager -> getNotificationByUserAndSpaceAndType(user, space, null) != null
b) NotificationManager -> isUserWatchingPageOrSpace(user, space, null)

Can you recommend which one I should use, for example regarding performance?
Are there any better options?

Thanks in advance!