Nessus no way !!!
From personal experience of me and some of my frens doing VA-PT
current nessus (Free version) is not good at all. Since they have
commercialised Nessus lots of good plugins are disabled in the free
version. And also found that the plugins which free version has also
not giving proper functioning. So I would not reccomend nessus (free
version)
Would like to get opinion from some one using Nessus Commercial
version.
Something about core impact.
This is much hiped software but if you are doing PT its very less use.
Since they have very very less number of exploits against the Network
devices (routers, Firewalls). And while doing VA no client has yet
allowed me to exploit there servers or other PCs :-D so its Core is
again not use for me there.
Best things I have found working are nmap, metasploit, separte
complied exploits, etc.