EFF, FSF, ACLU are all great organizations. ACM is unique here though because it's specifically a professional organization meant to push the industry forward. EFF, FSF, and ACLU are great and should be supported but aren't as broad as ACM.
If the ACM is really pushing professionalism and ethics now, that's great.
I've actually been a member or contributed to all the organizations either of us mentioned, and EFF has seemed to me likely a better predictor, but that's just a guess.
My biggest issue with EFF is that they often take pro-corporate positions and is lead by many actual executives and former executives (see board of directors https://www.eff.org/about/board), while the ACM comes more from an academic or tech worker strain (see https://www.acm.org/about-acm/officer-bios).
So while I agree with the EFF on many policies, their corporate leanings are a turn-off and isn't, imo, a solid ground for people doing day to day work in computing.
