there is no 'best' as that is a highly subjective idea.
Use Malwarebytes. It is not exactly antivirus, but complements antvirus suites very well, and can often remove stuff that many AV suites cannot touch.
The most popular antivirus is Microsoft Security Essentials as it is free, very lightweight, stays out of the way until needed, and catches most things (but has a hard time removing things if you actuially catch something). I have used it for a while (using Windows Defender in win8 right now which is the same thing), and have had no problems with it.
If you plan on finding yourself a virus then MSE will not do the trick. You will need some form of nanny-ware antivirus suite such as Norton which will do it's best to prevent stupid from occurring. It is expensive, it is intrusive, but it is also very effective if you need that level of protection.