Is it better to send a paper copy or submit it to http://grants.gov?
Either method is acceptable and you as the applicant should use the method that you are most comfortable with. If you chose to use www.grants.gov make sure that you have gone through the registration process at least two weeks before the due date. Once you have gone through the registration process, you will be registered and will not have to go through the process again for other grants or this grant process again next year.