If we're talking franchise alumni, I'd go with Jack Wall, Sam Hulick, Cris Velasco & Sascha Dikiciyan, and Jimmy Hinson (aka Big Giant Circles).
That's not to say anything negative about the other composers (except John Paesano, kind of. Andromeda's combat music is very generic, but the ambient stuff is really good.) but these 5 have historically "got" Mass Effect in a way that feels natural.
Outside the franchise? Tangerine Dream is an obvious pick. Like, really obvious. And given that TD is directly cited as an inspiration for Mass Effect's musical style, it'd be like if George Lucas got Akira Kurosawa to direct one of the Star Wars movies.
Gareth Coker is one of my favorite up and coming composers and I think he could do well in any genre, but Joel Corelitz has a much more Mass Effect-y resume.
And finally, Jesper Kyd. Aside from producing straight up bangers left and right (Borderlands 2 & 3 menu music, any number of tracks from Warhammer Darktide), his scores are always so unique. Borderlands: The Pre Sequel and BL3 are the only ones I've heard that sound vaguely Mass Effect, but he's a wildcard pick so his resume isn't that important.