you can watch it any order you want! however, i suggest starting with 1997 as it was made first and is the shortest of all of them (16x45 min) and was made first. second made was 1994 which is imo the weakest reply series, i just didnt like the dynamics of main characters so i havent even finished it yet. the most recent is 1988 which is again a really high quality and is as good as the 1997 series but is much longer (20x100 min) so it might feel a little intimidating to watch at first :D.
I strongly suggest to stay away from any spoilers! Reply series is one that will probably make you feel like you /need/ to know who is the husband but really, dont google spoilers :D
