i have tried norton av and now i"m using eset av and i have windows 7.so my opinion
resource usage:norton was using less ram but from time to time a little more cpu. result let me say tie.
real world system impact: eset is a bit lighter than norton
user friendly: both where user friendly so atie again.
user interface: i like them both,again tie.
level of protection:both very good
overall winner: for me i think eset is a little better.
p.s. i have used them both for enough time and i can tell you whatever you choose you wan"t do wrong both are great products
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p.s.2: norton now has 2 products 1)norton security and 2)norton security with back up. i think they stopped norton av and i don't know if that troubles you.
i hope i have helped you