Before making a final decision on what ISPs to use, you probably want to see each provider's Service Level Agreement (SLA). The SLA is the official commitment between the ISP and the client which defines particular aspects of service that should be provided to the client per the service contract. An ISP is not required to have an SLA, but many do, and many of them make their SLA available on their website.
The SLA may be part of the contract between the ISP and the client, or might not be. Aspects of service defined by the SLA can include such things as throughput, mean time between failures, mean time between recovery, mean time between repair, and uptime, as well as which party is responsible for reporting faults ...
