the as5300 is more of an 'access point/server' than a router. it has the ability to handle an array of port configurations from 2T1 to 8T1, etc. this is not a full fledged router with the routing and multiple functionality of a 2800.
the 2800 is a full fledged router that has the ability to be configured in many port combinations as well as providing full IOS routing, as well as many more features.
please see this link for as5300 info:
http://www.cisco.com/en/US/products/hw/univgate/ps501/ps503/index.html
please see this link for 2800 info:
http://www.cisco.com/en/US/products/ps5854/index.html