Sending a return on paper means that someone at the IRS will have to do data entry of all of your information into a fillable form before they can begin to see if it is correct. There is a backlog going back to last year's returns. I can't find the story I heard on the radio last week that talked in depth about this.

Filing it online meant a return was approved and the refund paid within 2 weeks. Free fillable forms work well, but you do have to figure them out ahead on paper to have all of the numbers ready to plug into the lines (and added forms).