What is the best antivirus program to use that is affordable and good?

i have about 3 viruses that are complete pain in the asses and i have been trying to get rid of them in vain for about 2 weeks. i really dont want to deal with it anymore so i was wondering how to do that operation where the computer is set back to its original factory settings and the hard drive is competely cleaned. my dad has been saying something about needing a disk to do this but im pretty sure ive seen my brother reset his computer without it. also, should doing this completely get rid of the viruses? thanks in advance  

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