RankerX is good for high DA Tier-1 backlinks: like web 2.0, social network and profile
You can check the site list and changelog, as they updated biweekly to keep it works for high DA sites.
https://docs.google.com/spreadsheets/d/1EN4bdBGOivxImq1NxWpCJZE9CWfDbj6Bg1drvGqV2RQ/edit#gid=0
https://medium.com/@rankerx/rankerx-change-log-6145e90b522a
GSA SER is normally for bulk Tier-2 or above backlinks creation, as it doesn't support most high quality sites.
Also, you need to purchase/scrape verified site list to create backlink effectively.
I used both of them as above cases. Remember you need Proxy and captcha solving service/tool like GSA CB or XEvil from XRumer to let them work. Hope it's clear and helps you.