I'd rather hire someone who is comfortable in any situation (mechanics clothes or business suit) than a rigid smartass who won't change they way he or she dresses no matter what...
One company was 100% casual (don't wear a miniskirt and you are fine). The company was the biggest POS to work for.
Another company is business casual (occasionally they don't mind me wearing a t-shirt and jeans) and it is is just a pleasure to work at this one.
Edit: I actually like wearing business casual, very comfortable cloths.