Yick. I mean, I love dresses and skirts on occasion but, in terms of practicality, they're a hassle. Car doors, cleaning and maintenance, and then there's the ever present problem of having to deal with chafing between the thighs. Most of the time, I wear jeans, exercise pants, slacks, etc.
On another note, in terms of passability, most chicks don't wear skirts and dresses all the time. Most girls I know/play sports with/am friends with wear skirts/dresses maaaaybe about 10% of the time, if that. The only women that I know who wear dresses and skirts more than that are either: a) very, very strongly feminine in appearance (South American chicks, southern black women, very old school old white ladies), b) Wear them for religious reasons (modesty, faith based dress code), or c) hippy chicks (though they wear them only about 30% of the time as opposed to 10%).
Honestly, dressing overly feminine is pretty stereotypically an early transition thing to do. I mean, if that's your style, cool, but do try to consider what 'you' want to wear as opposed to what you think is the most appropriate for a 'girl'. Do *you* want to be hyper feminine all the time? Will that work with where you're at in transition/with your features? What do you want your style to say about you?
Really consider all this before trying to slant your fashion one way or the other. Otherwise, you'll stick out in ways that will make you far less comfortable than wearing not-pants will make up for.