I think it all depends on the kind of product you are offering too: digital download? hardware? and so on. Besides, if you are in a country that's accepted by paypal, then you better go with that. Reason: Many online users have greater confidence in paypal because they are very robust and have been around for quite a while. So, check your country and perhaps your host could help you get the demographic view of where majority of your traffic/clients are coming from. This way you know you do not shut out your main stream (if you use a processor that does not accept payments from where majority of your traffic is coming from.)
Paypal is most widely used payment gateway so I think it is one of the best available for online payment receive and send
I am using paypal and moneybookers both are great payment gateways, but most of the time I use paypal
I´ve been using 2checkout.com for 6 years. PROS: 100% uptime service, never have had any trouble with payments. CONS: Not very clever system to avoid duplicated orders.