Why would anyone ever do it any other way??!!
By paying online, you have a guarranteed payment date. No more mail roulette. Do you know several card companies have actually been sued, because they were caught 'holding/delaying' payments sent in the mail?
You have to be nuts not to pay online, and that goes double if you put your payments in the mailbox instead of going to the post office. There have been so many cases of mail getting stolen from mailboxes, and CC payments are the big prize since it usually includes the CC numbers on them.