There are different takes on "best".
Best, for you is likely to be something that works well on your system for your browsing habits/computer usage, that you can understand how to operate and configure easily, that doesn't "throw a wobbly" with other programs you may use.
To this end, all the reputable security software providers should provide a trial period, usually about 15-30 days. Ideally its a full-featured trial (ie the trial software is identical to the paid for version) and should you decide not to use it, it uninstalls cleanly.
There are plenty of other seperate applications which can be installed, and are free. Some of them are darned good, and you can achieve at least as good, and sometimes better security with several standalone programs.
Most important is that you need to be able to easily learn what they do and how to respond to any prompts. So good help files/support forums (or company support that works) can be very important.
You can install the "best" security available. If you answer a prompt incorrectly, however, it can, ironically, leave you more vulnerable than if you installed a fairly average program that you find easier to understand.
Also of high importance is to keep all applications on your computer,OS included, up to date. A lot of the "nasties" find their way in through vulnerable software. Once a vulnerability is discovered, vendors are (hopefully) proactive in patching it.
My line up, for what it's worth, is all freeware. Avast AV, Threatfire, Comodo firewall 2.4, and a few other demand scanners. (They never find a thing. As it should be.) + Secunia PSI for checking that all software is up to date.