This is tough cause I love the entire series, even the mobile game Betrayal (which should be remade btw).
Since the usual suspects are being brought up I'll say that I really enjoyed Ascension (combat is top-tier for the Greek series, maybe even the best), and Ghost of Sparta (good story and Arms of Sparta are a fantastic weapon).
I haven't played Ragnarok yet. Will wait for a deeper digital discount (I'm in no rush to play it right now).
But I do hope that if the rumours of the series being remastered are true, that it's not just a simple remaster. I want GoW2018 sequel graphics, accessibility options, butter smooth 60fps (120 vrr) - just look and run better that's all.