The best "kind" of anti-virus to use is one that locks permission changes throughout the OS (often used in non-trusted, open access networks like schools and libraries). This is not what you're asking.
The "best" anti-virus for you is one that can detect infections from whatever risky source you throw at it (websites, downloads, USB drives, etc) and prevent your system either losing control or getting damaged. There are both free and paid software for this, so you just want one that does the job without worrying you about it.
Microsoft Security Essentials + Malwarebytes is a popular free combination. I suggest avoiding any software that begins with the letter A (AVG, Avira, Avast, AdAware) because my experience with them is that they're all easy to break (from a crackers point of view). Also avoid Norton and McAffee because they're over-sponsored piles of crap. I use Kaspersky myself, but ESET NOD32 is also one of the better commercial AV suites available.
In addition to a good AV suite, you also need to learn a bit about common sources of infection. USB devices very commonly get infected by worms that spread via auto loader. Some websites, and especially out-sourced ads in websites, can also infect you if you're not protected. Then there are email and IM worms, phishing sites, social network bots and sometimes key loggers (site-script-based, not local spyware). Learn about them, and you can help protect yourself about them (knowledge is power and all that).
Regarding salesmen... The majority do know what they're talking about, or at least what they're trained on. However managers are a different species of creature to salesmen - they care more about the figures than the customers. So salesmen are forced to push certain products and practice their sales pitch in influencing you into paying for their sponsored products. Also they're used to dealing with people who don't know a thing about the computer industry (the people silly enough to pay retail price for a computer you can build for considerably less), so when someone comes up to them asking if their products have certain features (like LTE or LTE+ in the Samsung Galaxy 3 phone I saw last week), they're struck dumb because what they're trained for is "it can do this, it is very fast, the price is very low, and if you buy from me today, you get a small discount and I get a small commission". They try to make everybody happy to push a sale.
This is coming from someone who sells jewellery during the day and advice on computers during the night. And also someone who has been on both sides of the virus-anti-virus war.