III ranks as my favorite one just because of the massive amounts of singleplayer content available and also as having been the one game where I felt the character creation was done correctly by having quite a lot of fighting styles reserved specifically just for custom characters. It also added to the RPG aspects of the created characters that you couldn't select actual characters' fighting styles right away and had to work yourself up to it.
I also really enjoyed Chronicles of the Sword as just a neat story being told with a similar feel to how Soul's story goes, but also with light RTS elements. It's always bothered me that they never did something like it again, though every year that goes by with no SCVI announcement makes me hope that they're toiling away on a new one in secret and they're putting a lot more effort into it than V had. Those storyboard cutscenes were just downright unforgivable for someone who actually likes the story, not to mention Patroklos is a shitty anime protagonist in a series where I felt archetypes like these have been decently avoided/subverted (though it also doesn't help that his English voice is Yuri Lowenthal).
I have this pipe dream of seeing a remade Soul Blade/Soul Edge, only instead of sticking with the stylistic choices present in the series now they go the full nine yards and make it super campy/arcade-y like the original. Seeing Edge of Soul remade in HD but with the song and everything would make for a great announcement trailer imo.