There are number of antivirus available in market.The most of the persons get confused when they try to choose.So please direct us and guide us here the best way to choose antivirus for different purposes and works.
This is a really vague question. Do you have a firewall?, for example. Does your company have an ftp site, customer web services? Are you UNIX only or lots of different OSes?
Most UNIX anti-virus applications do work reasonably well. And there are open source ones like clamAV, that are free. Go to SourceForge - Download, Develop and Publish Free Open Source Software
Based on your question and seemingly limited understanding of what you need: consider finding a security consultant. They do this for a living. All you need to do is talk to past customers of theirs to verify the quality of the consultant's work.
Or do it all by yourself and hope you get it right. Download and install something like clamAV. You decide.
I've used clamav. but some say it has small virus signatures database. perhaps you should get kaspersky or even norton.
I recommend OS-easy System Guarder. It is used for computer protection and backup. You can create many snapshots for different PC state. When your computer infects with virus, you can restore the normal state your want.