Web AS installation - Right Approach

Hi,

We are using SAP Enterprise Portal for web enabling content from SAP R/3, SAP BW and few other non-SAP systems.

As per my understanding SAP R/3, SAP BW and SAP Portal, all run on SAP Web AS (platform).

We have a single machine for all the applications (R/3, BW and Portal) to be installed (cannot be changed).

Keeping all this in mind, what is the best approach for installation?

1. Same Web AS instance for all the servers

2. Separate Web AS instance for all the applications (like one for portal, another for R/3 etc).

3. Any other approach???