Well being the same age as you I do notice how guys dress. That is only because I pay attention to how I dress and I try to dress in stuff that makes me look good, I don't justs throw on whatever is on the floor. But while I notice how guys dress, I don;t really care. I see past how they dress. The guy I like now dresses sporty because he is athletic. While I wouldn't pick out athletic dress as my favorite, it suits him because of his personality. And I don't even concentrate on how guys dress, it is more personality and if he can make me laugh. so basically I notice how guys dress, but I don't care. As long as they don't look like a slob it's all good for me.
Yeah a girl like me would prefer casual but I also love a guy who can add some flavor an style to it that really turns me on especially when they have plaid or nice colors.
As far as being more fond of one style over the other no. I like that guy for the guy not the outfit he;s wearing. I do care on presentation a little though. For instance the grubby haven't showered in days look is kinda disgusting. But little things like a few wrinkles or something, who cares?