The Oscar wins of Crawford and Davis or Lange and Sarandon?

I have yet to see Blue Sky (and I only saw 65-70% of Dangerous on TV years ago). The other perfromances are all wonderful performances, but I will give the edge to Davis/Crawford

The old Hollywood gals have a better 'set of wins', but mostly for Crawford's sublime turn. I would rank them:

1. Crawford, Mildred Pierce
2. Sarandon, Dead Man Walking

3. Davis, Jezebel
4. Lange, Tootsie

5. Lange, Blue Sky
6. Davis, Dangerous

She is. Few actresses (in history) have ever been so 'watchable' in front of a camera. So alluring (and I'm not even talking beauty-wise or sexually). She has a unique command of the artform that makes everything zero in totally on her and what she's doing in a scene. Little actions like sewing something, cooking, choosing which gown to wear, writing something down on paper... you can't look away from her, she's simply fascinating to watch. In addition she's the closeup QUEEN and had a surprisingly good knack for disappearing into a role, and a lot of different styles (western, melodrama, musical, comedy, horror). Despite what people (and Feud) may say, her pictures have aged VERY well. For some reason they took TCM Australia off of the air but even her less acclaimed vehicles that used to air, are great showcases of her graceful, brilliant, nuanced, delicate, transfixing performance style. 

I'm not Wendy, but I could recommend you some Crawford films if you wish. I grew up with them.

I would say 'A Woman's Face' and 'Humoresque' are essential vehicles for her. I think she may be my win for both in Best Actress (don't have my lineups), just two phenomenal displays of film acting. 'The Women' is a great, fun comedic villainess turn and the screenplay for that film is one of the best of the 20th century so i'd throw that in too for sure. After those i'd check out her two other Oscar-nominated performances in 'Possessed' and 'Sudden Fear', and then her brilliant late career lead in a Western, 'Johnny Guitar'. 

'Strange Cargo' and 'Grand Hotel' if you want to see her in younger, charming form (she so often played bitches). 'I Live My Life' and 'Above Suspicion' are also solid earlier efforts along those lines.

That's already plenty to see but 'Autumn Leaves', 'Flamingo Road', 'Baby Jane', and 'Harriet Craig' are also fun camp films that I have seen numerous times on TCM too. I find she actually grounds them a lot... you'll get to see her let loose in one or two sequences per picture, and will often get a good slap scene, but she's mostly very controlled and nuanced, managing to sell the more out-there moments brilliantly. Anybody expecting some campy over the top scenery chewing entertainment may be disappointed, she was more a maverick of a kind of 'streamlined' approach to melodrama. 

I know that's a lot of films but it's hard to recommend for her because she's one of those inherently watchable people (not unlike her 'Grand Hotel' co-star Garbo) where I could literally sit through a piece of dreck just mesmerised by her. I almost don't care how good or bad the movie is, she's transfixing to me. Even in some of her weird earlier musical roles.