A complete comparison of the two services can be found on this page.

In a nutshell, our "Basic" service lets you store up to 500 charts in your account and provides you with US real time data from the BATS exchange.

Our "Extra" service lets you store up to 200 groups (called ChartLists) of up to 500 charts in your account, lets you store annotated charts, create custom alerts, shows you longer intraday charts, and lets you create and run your own stock scans.

Our "ExtraRT" service is the same as our "Extra" service except that the real-time data comes directly from the major stock exchanges.  "Extra" and "Basic" get their data from the more limited BATS exchange.  (more details)

Our "PRO" service is the same as our "ExtraRT" service except with the PRO service you can create user defined index, have HTTPS secure access, create 300 ChartLists, 2500-pixel-wide Charts, quarterly and yearly bars and Historical Stock Data back to 1968.