FWIW, any others wondering, these are some things I’ve already found:
https://www.indeed.com/cmp/Seafarers-International-Union
https://www.indeed.com/cmp/US-Merchant-Marines,-Seafarers-International-Union
https://www.reddit.com/r/merchantmarine/comments/kcn30a/considering_joining_siu_or_msc/
Not too useful for making a decision, but interesting anyway:
https://www.indeed.com/companies/compare/Military-Sealift-Command-vs-Seafarers-International-Union-00e05fb9ac40a1fc-238f63f00126723e
It really sounds like the main differences are:
MSC you are much more likely to go beyond your expected duration on-ship. So away from home a lot more at a stretch than SIU.
MSC does sounds like it is a like more stable ref getting a ship–please correct if I’m wrong here. MSC folk do not have to go to a Union Hall and watch TV monitors for job calls (traditional Union thing, although I’m still confused why this is even a thing anymore–there really should be an app).
MSC has better benefits. For instance, if you need robust health insurance due to family members, then MSC is it.
SIU seems to have better pay. Please correct me if I’m wrong! I do not know if this means better base pay, overtime availability, etc. MSC job boards now are showing total average expected compensation that includes “all things pay.”
MSC you can hit the ground running, no 1.5 or so years of apprenticeship. They’ll take you as-is and train you as needed. Perhaps better room for advancement?? <<< Please correct if wrong.
SIU has their apprenticeship that gets you out the door with some nice benefits for the union–you can bid on jobs ahead of non-apprentice folk who still have their C book. I think you come out an AB? <<< correct me if I’m wrong.
Anyway, enough rambling, I’d love to hear from folk with relatively recent direct experience in one or the other (or both!).