Janet Suzman and Susannah York
I think these two ladies would have been my ideal Gudrun and Ursula.
Gudrun isn't supposed to be traditionally beautiful in the book, but she should possess a certain fire to become irresistible in certain men's eyes. I could never see the slightest m.appeal in Glenda, not even in a necrophiliac sort of way. Janet is certainly much more beautiful with her enigmatic, sphinx-like face and those incredible blue/purple eyes, but she's also the type of woman likely to be appreciated by intellectual admirers above all. And the feverish touch she can give to her characters, her burning eroticism, that "erupting volcano" feeling she possesses ... all makes me think she would have given a much more powerful performance than Jackson. I also think she's a superior and more charismatic actress overall, although she didn't have the same luck with film roles. I would dare to say Suzman was possibly the definitive Hedda Gabler of the century (tough btw her and Delphine Seyrig) and the fact that Trevor Nunn actually did a film version with Jackson while he was still married to Janet is baffling. I suppose the producers really wanted a bigger star. I can see some similarities between the two , although I find Janet to be more talented and attractive. Ironically, she gave a spectacular performance as Frieda Von Richtoven (Lawrence's wife) in "Priest of Love". A strong, Gudrunesque female who hugely influenced her husband's writing for years.
Any comparison between Jennie Linden and Susannah York would be quite unfair. Jennie was the weak link in the movie IMO and her involvement in it was some kind of lucky accident in an otherwise mediocre and completely forgettable career. She was lovely and feminine and, because of this, she worked in certain ways and didn't really ruin the movie, but her most dramatic and intense scenes would have required someone with superior authority and command of the scene. Susannah would have been perfect: she possessed that kind of delicate, classical beauty that made her an obvious choice for most literary heroines, but at the same time she had an unmatchable grit that allowed her to hold her own against the most accomplished of co-stars since she was in her early 20s. So she would have been wonderful as Ursula. I think Charlotte Rampling could have also been a good choice, although she was possibly a bit too young.
On the other hand, I think the casting of the male leads was perfect. I doubt anyone could have been as exceptional as Bates at playing Birkin and, even if I could think of other actors that would have been as good as Reed at playing Crich, Ollie remains a winning choice.
And no one else than Eleanor Bron as Hermione!