What is the best practice for busy web application?

I have a web application that is about to see some traffic. Here are a few approaches I've thought of, but I don't know which one is best:

• Multiple VMs each with own files, with a Varnish front-end load balancing them
• Multiple VMs with a shared NFS on separate VM, with a Varnish front-end load balancing them
• Multiple VMs with a shared NFS on host node, with a Varnish front-end load balancing them
• One powerful VM, with Varnish acting as reverse proxy

Can you please advise which is the correct best practice approach?