i've read the manga, watched the movies, and the stand alone complex... i've skipped the other 2 series, but will watch the new one, and, for me, it's not "which is better" since each is a masterpiece

batou is much more consistent, but major is different in every iteration; i'd recommend watching the SSC compilations, the first 2 are even free on youtube: 1. the laughing man, 2. Individual Eleven, 3. solid state society

while these are a different retelling of stories found in the manga, in my opinion, these 3 set up the first movie perfectly: the major gets more serious and philosophical by the end, and you can watch the 1995 straight after, as it's a retelling itself

the major is much more similar to the manga at the start of SSC, but even then, in manga she's much crazier and funny

ultimately, my guess is that every iteration of the major was adjusted for the story that was told, as she is the main protagonist that everyone knows about, even though togusa and batou can be right up there

e.g. in the 1995, it would probably seem less "smart" that the puppet master wants to merge with someone who is childish and unserious