Well the two companies that you asked about are providing two separate services.
2CO is a third party processor. While they might have a few unhappy customers, they have a lot more happy customers. You have to remember - people tend to complain more than they will give any one or company a compliment. You would also need to check 2CO AUPs to make sure that what the merchant is selling is OK with them
Verisign - actually Verisign's Payflow - is an electronic payment gateway - similar to LinkPoint and Authorizenet.com. It is not a merchant account provider (MAP). You still need one of these to fully accept credit cards unless you choose 2CO.
With 2CO, their name will appear on the consumer statement instead of your merchant's. They pay every 2 weeks (unless you are process about $1,000 a week). With a merchant account, you usually get your money 24-48 hours after the saile.