PayPal is by far the first and foremost payment processor, at least in higher-tiered countries. I would say AlertPay and MoneyBookers follow, but neither of them come anywhere near PayPal in terms of popularity.
PAYPAL is best for me becuase i used this method since last two years.... It is safe and secure site and accepted in the world by the people...
Everyone has and uses paypal so you'll be "dead" without an account there, my businesses increased a lot since I signed up on paypal