My company is a bit unhappy with the support we've been getting from Cybersource and we're about to embark on a billing re-write so we're taking the opportunity to look at other gateways. Anyone have any positive or negative experiences they'd like to share?

I'd rather not hear about small website gateways like paypal, we run tens of thousands of transactions and millions a year. If you know, I'd love to hear how much you're paying in transaction/gateway fees too.

We're primarily a .NET shop if you'd like to speak to a particular API. Gateway must support the big 4 credit cards (mc, visa, disc, amex) and ACH.

Thanks in advance for the help from the hive mind. :)