Portal Migration to 7.3 or Upgrade

Hi

We are going for an SAP Portal Upgrade from 7.0 to 7.3 but since there is a lot of change that happens in portal from 7.0 to 7.3 the current functionality will have to be modified, so we are thinking of Building a new portal 7.3 system and creating new contents and migrating some old contents in it.

Which would be  better practice migrating or Upgrading  7.0 to 7.3

Thanks and Regards

Tushar