I know a few people who don't even read comics but like Superman, can't say the same for spiderman. I think Superman needs to go through some changes to keep the popularity with the newer generation. I mean look at smallville I know loads of people who watch it but they don't know a thing/ care about Supes.
Ten to twenty years ago it would have been Superman but I don't see how anyone could even make an argument for Superman being more popular then Spider-man right now. When was the last time you say a kid with a Superman t-shirt/shoes/random merch? Spider-man's face is all over the place and it has been for a while now. I'd even put Batman above Superman's popularity.
Honestly, it really isn't even a contest, Spider-man is hands down the most popular/well known comic character.
Spiderman is very popular among alot of youth but if you look into the general public most people know of Superman more. He has been around longer has had more media coverage from Movies, animated shows, and even Reality TV series.
While in comics he may be slipping overall he is still tops in drawing power.