I think models and actresses can share covers 50-50.
Actress covers are generally very bland these days (save W occassionally), but I am not too thrilled about the models who have the strongest prospects of making the US cover either: Daria Werbowy, Isabeli Fontana, Karen Elson, Liya Kebede, Carmen Kass, Karolina Kurkova, and Caroline Trentini. Their work in US Vogue is SO routine.
Models that I do want to see, with photographers on contract with Conde Nast:
Julia Stegner (ph: Raymond Meier)
Diana Dondoe, Elise Crombez (ph: Steven Meisel)
Natalia Vodianova (ph: Patrick Demarchelier)
Gemma Ward (ph: Craig McDean)
and of course, Gisele Bundchen (ph: Mario Testino)
As for celebrities, I have a couple on my short list:
Keira Knightley, Kate Beckinsale, Stephanie Seymour, Naomi Watts, Rachel Weisz, Thandie Newton.
Zhang Ziyi can make Elle first.
Kate Winslet has never had a Vogue cover. Not that I think she's a style maven, but she's a better choice than Drew Barrymore or Liv Tyler.
A couple categories for SHOULDN'Ts:
Fifteen-minute famers: Mischa Barton, Jessica Simpson, Sienna Miller, Kate Bosworth, Lindsay Lohan, Emmy Roussem [sp]
Over your quirks: Chloe Sevingy, Maggie Gyllenhaal, Sofia Coppola, Selma Blair, Vanessa Paradis, Christina Ricci, Charlotte Gaithersburg
Just so embarrassingly overexposed: Sarah Jessica Parker, Renee Zellweger, Beyonce Knowles, Gwen Stefani, Sheryl Crow, Catherine Zeta-Jones