best antivirus download

Personally, I think Avast is one of the best at the moment. Just choose a "custom" installation and make sure that everything except the three "shields" are ticked during the installation so you don't install useless bloated stuff.

https://www.avast.com/en-gb/index

I moved from Avast, which is excellent, when it had the blip that gave problems to some PC's.
I started using Bitdefender (HERE) and found it to be excellent. It's quiet as well, just runs in the background and updates itself. Does an auto scan quickly and silently periodically. I never bothered going back to Avast.
If you just want to install and forget, Bitdefender is good.

What about Kaspersky?

I can't personally vouch for this Chinese offering but it does get pretty good independent reviews.

http://securitywatch.pcmag.com/security-software/321857-chinese-antivirus-qihoo-360-earns-top-score-in-independent-test

Recommendations of which AV product to use are, of course, subjective. What suits one person's browsing habits may not offer enough protection for those who are less careful about the sites they visit, links they click on and programs they download.

There are a number of very good anti virus products available both free and subscription based but none of them can ever offer you a 100% guarantee that malware will never get onto your system. You, the User have to play your part and as boring as the subject is, your best defence is to back up your system or your important files regularly. Then, if the worst happens at least you will have the security of knowing your important stuff is safe.

Anyway, back to the subject of "which anti virus is best". Of the three main independent anti virus testing labs that most techies will pay the most attention to, namely: https://www.av-test.org https://www.av-comparatives.org and https://www.virusbtn.com all do regular updates of test results using huge numbers of old and new malware threats across the main operating system platforms.

AV-Test's latest results for Windows 7 are here:

Results for Windows 8/8.1 here

Later tests for Windows 8/8.1 are detailed here

and for those on Windows 7 here

My suggestion is take your time to read the reports and then experiment with some of the different offerings that rank highly. Many of the subscription based programs can be downloaded on 30 day trial periods. As long as you uninstall the one you've been trialing before trying another you can try as many as you like to find the one that you feel most comfortable with.