Let's look at it this way: Brawl had 3 girls playable.
Peach, Zelda and Samus (Sheik and Zamus don't count because they're the same as two of the other girls).
Nana doesn't count because she's second fiddle to Popo. (You could count this as one half if you want).
Jigglypuff doesn't really count because it's a Pokemon and, well, it's had to tell. Not exactly a blatant example of femininity. (But she actually is a girl, so count if you must).
SSB clearly needs more girl than 3 (or 4 and a half).
Though, that obviously isn't a reason to put a character in the game. People just want more girls and that's fine.
There are also a number of characters who are genderless/have an unclear gender. Kirby, DeDeDe, Meta Knight, Squirtle, Ivysaur, Charizard, Pikachu, Yoshi, ROB and Game and Watch. (I know most of them DO have genders, but I them consider foremost as animals, Pokemon or sexless marshmallows in the case of Kirby.) It's harder to see the Male/Female situation with all the of the characters that are animals/creatures. Taking that into account things are less skewed in favor of male characters.
Character opinions:
I would personally like Krystal just because she would (hopefully) shake up the Starfox clone format.
I absolutely want Midna over Tingle. I mean Tingle's funny, but really? Midna & Wolf Link combo would be great. I highly doubt that would happen, though. It would probably come down to Tetra V. Tingle. And Tingle's AT inclusion was really just perfect - it hit the nail on the head. I fell that's the best use of him. Tetra or Midna would be far better in my opinion.
Lyn is an option, but I don't see it happening. Just due to her older status in FE. (not that that's a real reason.)