Authorize.Net ARB is a standard recurring billing system module and gives you the freedom and flexibility to accept recurring payments without the need of a bulky shopping cart system. The users opting ARB payments mode will be charged the first amount of payment the next day after they subscribe on website, then the recurring billing will start after the first membership period.
Paypal too is an online payment gateway but the process is too length for a transactions to complete, fee for multiple transactions, no recurring payment options, cannot make a change in the amount variations on subscriptions.