Personally, I would prefer Authorize.net over Verisign.
Authorize.Net is far more universally compatible with 3rd party systems. It is also very cost effective for everyone from the small business and up. Authorize.Net has over 100,000+ merchants and processes over a million transactions per day at its peak.
Verisign is compatible with a lot of 3rd party systems but not as many as Authorize.Net. It has some more robust reporting systems that some larger corporations may prefer and it has more free included transactions - but it is also quite a bit more expensive.
There are also a number of other good gateways available such as eProcessingNetwork, Paradata, Cybersource & iTransact. In my experience, each one of them has its own strengths so it really depends on your list of needs as to which gateway will be the best & most economic option.
CDGcommerce.com - Trusted Merchant Account Solutions since 1998
Many thousands of successful, growing businesses benefit from our expertise every day. You can, too!
We help merchants to eliminate gateway costs, reduce & mitigate fraud and achieve streamlined PCI compliance. Learn more today at http://www.cdgcommerce.com - we look forward to helping your business grow!
Each gateway has its own issue. We have worked with Authorizenet.com, LinkPoint, and Payflow (the gateway made by Verisign).
I would choose Verisign over Authorizenet.com - it actually could be cheaper because you get 1,000 free transactions a month which could mean about $100 (1,000 times $.10). Working with Payflow, one thing that I have noticed, when you make a change on the control panel, it takes about an hour before it to become active. Being in the internet age - we expect things in real time.
I think Verisign (Payflow) has more brand recognition with consumers so it might be better from the standpoint of letting your customers know that the payment gateway is provided by a company they know and trust. Also, as Corey mentioned you get 1000 free transactions a month which can save you a bundle.