It is a very complicated job to search for the best antivirus software from the list of hundreds. It is not important that the most costly software will provide you best protection against threats. You can choose the best for your use depending on its features. Some features of antivirus programs are:
On-demand scanner: The most basic feature of any antivirus is scanning on demand. It scans your whole computer or specified folders checking the virus contents in them. You can schedule the time to run this program or can run it manually when you want. The antivirus software needs frequent updates because this scanning facility will search only for the viruses available in its database. So to update the database with latest viruses you must update the software time to time.
On-access scanner: This program runs all the time and checks the files about to open for viruses. In this way your computer will not get infected with viruses if you forgot to scan any file. This program is very beneficial for commercial purpose but automatic checking of files will slow down the speed of the computer.
Email scanner: This program checks the email for viruses before it gets written to the disc. It also detects the viruses come with attachment in mail so protects you from viruses spreading through mail.
Web scanner: This feature checks harmful content in websites. It will automatically check the web pages for dangerous content. It is not an essential feature because when any content is downloaded from webpage gets scanned through access scanner. So it is not important that the antivirus software has this feature.
P2P and IRC scanners: There are some antivirus software programs that provide filters and scanning services for P2P and IRC file sharing. It is not an essential feature as the threats in the file can be detected by access scanner.
So all the antivirus software programs have different features and you can choose the best to buy according to the features useful for you.