Service level, cost, and technical application are key points. If you simply want Internet connectivity for internal office use, I would focus on cost. It might be most cost effective to get cable and DSL and implement redundancy using a router.
You can quantify the cost to the business from loss of connectivity, which will allow you to better weigh the ISP's SLA versus cost. If having Internet connectivity is critical for all employees' workflow, you could consider the cost of payroll for an hour versus the SLA for the connection. If most of business is conducted independent of the Internet connectivity, a cheaper connection will have better return on investment.
If you are going to be using the upstream but serving the Internet or uploading a great deal of files, there is better technical argument for the bandwidth of a professional connection.
In my local market the cable providers are more than capable of providing Internet connectivity for an office.