Using NSFileManager is the preferred way as written in the Docs: Foundation Functions Reference (NSSearchPathForDirectoriesInDomains)
You should consider using the NSFileManager methods URLsForDirectory:inDomains: and URLForDirectory:inDomain:appropriateForURL:create:error:. which return URLs, which are the preferred format.
I don't know if there are any real drawbacks when using NSSearchPathForDirectoriesInDomains
to determine the URL to your documents directory. I would recommend to use NSFileManager and it's method as this is the quasi-convenient way.