hits are "useless" ----
unique visitors are most important.
a hit is EVERY object on your webpage, images, style sheets, the page itself, and few other things.
If a webpage has a style sheet, 10 images and a person went to that page... it would be counted as 12 hits.
now, visitors and unique visitors and visits --- this can be counted different for different stat programs, but in general:
a unique visitor is for a given period of time and this visitor can have multiple visits.
good luck