The closed deals report by lead source will show you which of your marketing is most effective at producing closed deals in a certain timeframe and the commission generated as recorded in the deals feature.
Finding this report
To access this report click Reporting > Lead Sources > Show Me Dropdown > Which lead source has the most closed deals.
Report filters
In the top right hand corner you can select a different reporting timeframe and you can also choose between reporting for just web leads, manually added leads or all leads.