the less you compress it the better it is
and yes need to know more of what you have and what media you want to save to
example
avi 750mb to mpeg 2 saves out to almost 3gb some software even higher
if viewed only with pc or mac stick with avi it's for high compression and good quality
a dvd at 4gb is a mpeg format can be saved on avi at 1.4gb without loss