Hi Pas,
There are other levels as well.
On my current project we are currently using Application Component but setting all rules applications to the same component hierarchy code. This gives us much the same effect as global without some of the downsides that come with moving between global and other access levels (we previously came across some performance issues).
It also means that if we change our minds later, or want to create another group of shared rules applications we can easily do that without impacting the original combination.
Btw if you are looking at a potential multi-deployment scenario, where some of your rules might need to be shared to more than one SAP server (e.g. CRM & ERP, SRM & ERP, etc.) then make sure the component you use exists in both systems. One of the basis components is usually good for that, e.g. BC-SRV-BR itself.
Rgds,
Jocelyn