The standard bundle includes AV which allows you to protect a web server from http/ftp uploads of malicious files using the AV database.
The Advanced bundle includes the Cloud Sandbox feature which supplements the AV database but running the file in a sandbox for better analysis and is more accurate in detecting 0 day viruses.
Below are the features you get with each bundle:
|Standard Bundle (24x7 FortiCare plus AV, FortiWeb Security Service, and IP Reputation)|
|Advanced Bundle (24x7 FortiCare plus AV, FortiWeb Security Service, IP Reputation, FortiWeb Cloud Sandbox, and Credential Stuffing Defense Service)|