What kinds of internet speed does Comcast internet service provide?

Depends on your regional bandwidth that is available. In some areas Comcast is faster than other ISP's ... in other areas it is not as fast.

if you live in a DOCSIS 3.0 updated area and subscribe to the normal performance internet you will receive 12 mbs down and 3 up. non DOCSIS 3.0 area performance internet is 6mbs down. economy tier internet from Comcast is 1 mbs down. comcast also sells internet speed up to 50 mbs