Dare I say that Tifa looks more masculine than Rinoa, at least when comparing those two pictures?
Tifa's face, while still obviously that of a females, has a no-nonsense, strong, straight nose that reminds me of Seifer or Squall. Rinoa, on the other hand, had a very thin, delicate nose, with a tiny bit of an upturn at the end.
As said, Rinoa has a fuller, heart-shaped face, while Tifa has a long face compared to her. Tifa jaw-line and chin also seem to be much sharper and more drastic, adding to the 'masculinity' of her face. I honestly think it suits her though. I never pictured Tifa as a frail waif, like Rinoa, but as a girl-of-the-mountains, with strength in her features.