Originally posted by Laura:
The differences between the two dresses has lessened greatly in the past few years, but in general:

Smooth dresses don't have much in the way of drapey scarves or floaty bits. These would tend to get tangled up during the fancy American-style moves. Smooth dresses are slit over one leg quite often. The skirts on Smooth dresses tend to be fuller than on Standard dresses, but the difference these days isn't what it once was when dancers would do moves where they'd practically lift their skirts over their heads.

Because Standard dancers don't break from the regular dance hold, the backs of the ladies dresses are emphasized. Also, having large floats dangling from the right arm (among other places) is becoming quite popular again. Standard dresses are rarely ever slit.

If you're a beginning-to-mid-level dancer and can only have one dress, it is quite possible, practicle, and acceptable to have one dress for both styles.