DS3 is a 45 megabit per second circuit and is service sold by major telecommunication companies such as AT&T, Verizon, and Sprint.
The speed of a DS3 is symmetrical, the same speed in each direction, 45 meg upload, 45 meg download.
Cable companies such as Comcast do offer what they brand as "business class" high speed internet access. However the maximum speed is usually 8 megbits, much less than DS3. Furthermore, the speed of the circuit is asymmetrical, such as 8 megabit download speeds and 1 megabit upload speeds.
This asymmetrical bandwidth is usually fine for business who only want internet access for their employees to surf the web, where most of the traffic is download, not upload. On the otherhand, if your business is hosting web sites, you would not be served well with cable because the upload bandwidth will not be sufficient to provide fast access to your web sites.
Keep in mind the future needs of the business. If you go with a fractional DS3, you can get it with burstable service (meaning committed rate is something like 15mbps, but you can burst for short periods to the full 45mbps). You can also easily upgrade your DS3 to add more channels, increasing bandwidth. With the business-class cable, they only offer you the one speed and it cannot increase beyond that limit.
Also, the DS3 will probably provide better features such as the ability to run BGP against your provider (if needed).
Keep in mind that the DS3 services will also be more costly than the cable services. You are paying for SLAs and additional services.