two other options which are also "the best" or at least "very good" are BitDefender 9 and AVG Free. AVG Anti-Virus is highly rated and as the name implies the AVG Free version is just that, free. I have been using BitDefender 9 Professsional Plus since it came out. i switched to it from Kaspersky, after a brief flirtation with F-Secure and NOD32. surprisingly enough, BitDefender scan found three viruses and two trojans that Kaspersky, NOD32, and F-Secure all missed, despite each being on the latest definitions.
personally, my #1 recommendation for pay-for antivirus is BitDefender 9, not only because of it's excellent virus detection and removal (as i said it found things that none of the other three did), but also because it has an excellent firewall, and on-access virus scanning (meaning it automatically scans every file and process accessed by the computer/user; but this does not seem to have any impact on system resources, at least not noticeably on my P3 1.0ghz w/ 512mb PC133 and Win XP Pro), completely automatic updates, and great customer service. and at only $40 for BitDefender Pro Plus, it is very cheap compared to some competitors.
however, if you don't want to pay for an anti-virus, AVG Free is excellent, it is capable of removing all it finds and is better at detecion then NAV/NIS or any of the most popular ones (that have over the years evolved into nothing but bloatware resource hogs). slow computers also like AVG becausae of it's super minimal use of syetm resources. i personally install AVG Free on all computers that i sell or repair for people (that don't already have an AV or have a very outdated one) and recommend it to anyone who wants good, free anti-virus.
so as far i'm concerned it's whether or not you want to spend $$$. AVG Free if not (as i said it is great for being free), and BitDefender 9 is you are willing to spend $$$.
now, you also mentioned anti-spyware. unfortunately, this is seperate thing. though most AVs scan for spyware and malware as well as viruses and trojans (BitDefender also has the highest malware-removal rating of any), this is just supplimentary. if you want true anti-spyware, you need seperate software. the best anti-spyware solutions avalible are Ad-Aware SE Personal and Spybot-Search & Destroy. when used together i have found these two to catch anything thrown at it. and best of all, they are both free.
spybot-s&d download (from home site):
http://www.safer-networking.org/en/download/
ad-aware se personal download (from home site):
http://www.lavasoftusa.com/software/adaware/
bitdefender home site:
http://www.bitdefender.com/
AVG Free download (from home site):
http://free.grisoft.com/doc/2/lng/us/tpl/v5
some AV reviews (supporting what i say about the one or both of the two i mentioned being the best or at least good):
http://anti-virus-software-review.toptenreviews.com/bitdefender-review.html
http://www.pcworld.com/reviews/chart_test_report/0,chid,6214,prodid,27537,00.asp
http://www.pcadvisor.co.uk/reviews/index.cfm?reviewid=231
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