A web app as its independant upon which OS it runs on, only browser compatibilities are needing to be dealt with. Its easier to update then having multiple apps on local workstations. Scalability is better but depends on the server resources.

Using a local win app is harder to keep all workstations updated but its dependant upon the workstation resources and OS for its issues. Also, it can be better performing as its all client side and only dependant upon the server's database and not IIS.

So depending on your environment and plan of scalability, you have the info to choose which is best for your situation.