Anyone who thinks Spider-Man is more well-known is either a fanboy or isn't thinking clearly. According to Time Magazine, the Superman emblem is ranked right after the cruxfix in worldwide symbols. The FRIGGIN CRUXIFIX. That's how well-known Superman is. EVERYONE knows who he is. A popular movie does not instantly generate into more notoriety. Superman has been well known for the last fifty decades.
Now as for popularity:
It's simple statistics. Superman simply has a larger pool for people to like him (and dislike him as well).
Let's say the world's total population is comprised of say 100 people. 30 people know Spider-Man and all 100 know Superman. Let's say twenty percent of the people who know Superman don't like him and only 2% of 30 people don't like him. Who is more popular? Superman. Let's say 50% don't like Superman and only 0.2% don't like Spider-Man. Who's more popular? Superman.
Simple law of statistics. Superman simply has the larger pool to draw from.