I've looked at some similar questions on here, but we have very specific requirements and do not have the technical expertise to figure out how to map other questions to our situation.
We are willing to pay enterprise prices, but we need very high accuracy rooftop geocodes. We would be submitting individual CASS-validated addresses, as many as 15k an hour, and requiring low-latency results. We require a very high uptime. For TOS, we are not a profit-making entity, but we require the rights to store the results. Preference would be given to services that are better able to keep up with new development. Domestic addresses in the State of Wisconsin are required, other domestic addresses and international addresses would be nice. We have no need for reverse-geocoding. We have a use for batch-geocoding but only if expected accuracy is very high (our individual geocodes are human-verified; batches would not be). Responsive customer support is a big plus. Ideally the cost would be less than $5000/year, but accuracy and availability are the two biggest concerns.
I've looked at several companies that provide these kinds of services, and the problem is that our GIS specialist has left, and we lack the technical expertise to evaluate the accuracy of these geocodes. In the interim we are using Bing, but have received many complaints about the accuracy of its geocodes.