I wasn't allowed a Barbie doll growing up, and was finally given one by Mum at my 21st! I think Barbie is awful and Bratz are even worse and we will be avoiding them.
If, however, DD is desperate for one (as little children so often are) then I will get her one I suppose. I think its important to teach your kids to critically evaluate the media, so discuss what they see on the telly, magazines, toys etc.
You can teach preschoolers that ads on the telly are not 'real', that the people who make ads are trying to make them spend their money etc, and you can ask things like "gosh, Barbie looks very skinny! Do we know anyone who is that tall and skinny? She must surely be ill! etc.
Likewise we can 'immunise' our kids against sexist stereotypes etc ("all the Mummies in this story book are cooking...who does the cooking in our house? Does daddy sometimes?)
Having said this, I do think Bratz (and Barbie, and mini skirts for toddlers, and PADDED BRAS for little girs) are awful, creepy and, actually, just plain wrong, because little girls are little girls and not little women.