They are basically the same magazine: Same layout, same type of coverage, same deadlines (they are both weeklies). Time has a circulation of slightly over 4 million and Newsweek has a circulation of a little over 3 million.

Of course, their coverage varies week-to-week. I personally prefer Newsweek...there are some columnists and features (the "my turn" column, for one) that differentiate it from Time. But if you are looking for a quick, easily digestible way to see what's in the news that week, either magazine does the trick.