The main problem with the paper element type of filter is who and where it is made and the size of the unit. The small "Made in China" element filters and the small diameter chrome holders they make can tend to choke down your engine just enough to not be noticible, but enough to cause your engine to run rich and disrupt the gas milage you expect to have. Eventually the plugs fowl and the truth is known. With a proper oil bath air cleaner, this problem can usually be avoided due to the fact that they are sized correctly and air restriction is not an issue.
Joe
