Best online all-in-one is probably moz local or yext
These are automated......and aggregated so takes longer for listings to change...........there are also manual solutions where the listings are found and you edit.....like brightlocal
Make sure you read reviews for the services you use so that you are aware of potential issues.
Doing it yourself obviously helps you learn how everything works, the data is correct, and allows you to take advantage of other possibly helpful features many directories/listing sites offer beyond just NAP.
but you need to familiarize yourself with who is who in the listings food chain and start at the top.....
i hired a summer intern a few years back and had him go through them all and take control of each listing. We set up a spread sheet with all passwords and locations.
He did all my socail sites also.