Hi!
It's quite hard to compare those two tools, as every tool is different and have different use.
But i can tell you what make them different:
-price - ~90$ one time payment for GSA SER and ~70$ monthly payment for MS
-work - gsa ser is fully automatic and MS requires work for setting up everyting, adding new sites and not so rarely to fix issues
-links - magic submitter create less kinds of backlinks but usally stronger ones, and you can add own platforms to make it more effective - GSA doesn't need it
-speed - you have to harvest or buy lists for magic submitter but then it will run way faster, and it's faster overall i think. However you can still add own list for GSA.
Overall, if you have money i'd say but them both. But if not, analyse your website and competitors size - GSA is better for smaller sites, magic submitter for bigger ones.
That's my opinion - good luck!