Depends on which one you are using...But Most of the brand name one's are large and are bloatware...Mainly there updating and scanning will slow down your computer and how much of your system resources it is hogging up..You mainly want to stay away from, Norton/McAfee/ and anything over 100 mb on download..
Its depend on your antivirus software that how good is that and about the capacity of that software. You have to choose any updated that capable to detect & remove the latest viruses....
Avast, Lavasoft Adaware, AVG, Kaspersky, Malware Bytes are all good ones that won't bloat your system
