Hi.
I technically tested both with Kaspersky and Symantec for VSCAN on ONTAP 9.1.
To be honest technically the vendor itself not really playing a part. It can help with reports mainly, and has different type of scanning... but everything else is controlled by ONTAP - so I don't think you'll find any actual difference if you compare between the engines.
As for licence cost, I think here you better compare and do workload tests. i wasn't involved with the first two vendors, but with two others we looked at later on last year - If I recall correctly:
One was £2500 per McAfee scanning server. +£300 per year for support.
And another quote was for TrendMicro with £10 per user per year regardless the number of scanning servers. .
So it's two complete different approaches for licencing - each will better fit to different customer - with a significant cost difference depend on the amount of scanning servers/users and the contract length...
Let me know if you have any more questions.
Gidi