Inventory Solution tells you what software is installed.
Application Metering tells you who is using the software, and provides the ability to prevent a user from running a piece of software.
Inventory Solution plus Application Metering = license harvesting.
Software Management Solution provides a basic license count feature as well as allowing you to create and deploy software packages in various forms.
Asset Management Suite provides feature rich license, contract, and other asset functions.
So, to answer your question, you will most likely be best off with using Application Metering unless you wish to either replace an existing asset management tool or have a second one.