big. the main advantage of a smaller sprocket (aside from weight) is that it's "out of the way" for grinds and such on street. personally i despise the new small gearing trend. everything wears out so much faster when you run a small sprocket and small cog because there are fewer teeth taking the abuse of just pedalling the bike, you're also putting a lot more torque into it because the crankarms stay at 175mm or 180mm while the sprocket is smaller, which leads to even faster front sprocket and chain wear.
a friend of mine uses a profile cassette hub and he's had to replace the cassette body at least once since he got it about a year and a half ago. it's a sweet hub though.
i prefer the tried and true 44/16 gearing. the weight you'll save with smaller gearing is neglegible. it's just a trend. a stupid, stupid trend.