From personal experience ESET. We'd used ESET's NOD 32 (without Smart Security's firewall) which worked lightly & unobtrusively on Windows 7 SP 1.
Currently we have Kaspersky Internet Security in place. It is a strong and worthy contender which has been in use for just three days. Alert windows warn that the SSL connections for regularly visited sites, Google (Voice/Gmail) in addition to our Banking site, may not be secure. This feels reminiscent of UAC warnings, but rather than annoyances they are clear reminders all may not be as safe as we'd wish to believe.
My first choice would be KIS & second choice will be ESS.
ESET's NOD 32 is feather light as specified By @Cats-4_Owners-2.
If my only need is a real-time protection then my first choice will be ESET's NOD 32 without any hesitation.
Resource Usage (eg: CPU, RAM) > Nis
Real World System Impact > Nis
User Friendliness > Nis/Kis
User Interface > Nis/Kis
Level of Protection and Features > Nis but Kis also provides excellent protection
Ok..Norton fanboy here
Since I am satisfied norton's customer so my vote goes for Norton but that doesn't mean the others are not good though, it's just based from my personal opinion, anyway these are my opinions ( never try K7 and Trend micro, so i can't say anything about these products)
Resources usage > Nis
Real world system impact > Nis
User friendliness > not really sure about this, they are all looks good and user friendly in my opinion
user interface > Nis definitely
Level of protection and features > well..when it comes to "Protection" so that's basically means not only about "detection" right? if u are talking about detection then Kis and ESET better than Nis, but when it comes to whole protection and features I think Nis won due to Sonar, excellent file reputation, download insight and firewall. Kis has firewall and application control which is also good, and ESET has pup/pua detection, but assuming you are an advanced user which can deal with fake installer/adware installer and assuming you are not a "next next next" type person...then I think you don't need this feature, so..regarding this matter I too vote for Nis.
I personally prefer ESET over all the above as @exterminator20 stated. But Since i had to switch to KIS due to ESET License exp, i am getting the equal rating of it. So i would like to say KIS is also good but not the best.
One can only use published test lab results as a guide since what components are tested and how they are tested varies from lab to lab. Consider, for example, that KIS always performs towards the back of the pack in Virus Bulletin testing while at the same time always places in 1st slot when tested by MRG.
To confuse the potential user even further some AV tests are performed with default settings, others at maximum settings. This seemingly minor detail greatly influences results. In other words, AV at default settings may perform significantly better at max settings.
Plus I'm not convinced that AV lab testing is not biased in one way or another.
Both KIS and ESET have a long-standing reputation here at MT.
KIS has better removal routines than ESET...
Kaspersky support is located in India. ESET, I think, is still Czech-based ... but I could be wrong on this detail.
(Personally, I have a difficult time understanding some of the Asian sub-continent accents. My ear is not trained. I think ESET support is more polished ... and generally a more refined product overall.)
Kaspersky is the technological leader (especially digital forensics)... and I do not know how anyone could refute it (but this is MT and there is someone...I'm sure of it).
KIS is only available in 32 bit version (32/64 compatible).
Performance impact ... will depend upon hardware of specific system.
But it is funny how, when softs is installed on system, personal preferences become more important and trump a lot of technical specs.
K7 is good security software but still needs to improve their overall performance in such real world testing.
For such simplicity at its finest where install and forget feature implemented then go either Norton or Trend Micro since online reputation based already activated primetime.
Meanwhile ESET as mentioned already even before, the characteristics like fast response and solid protection from realtime and web shield is also implemented. Kaspersky does provide optimum protection alongside of tweaks you can do and other features you may wanted to try them, removal feature of threats is one to be intensive process for KIS that makes it effectively handle on any infections.
From my conclusion Norton or Trend Micro for simplicity, ESET for conscious in having latest threats as possible, Kaspersky for balance security software.
my choice is Eset is lightweight and has excellent detection, as well as at all the remaining programs are also good, but the choice belongs to each individual.
Kaspersky although the second is for my hardware is a little too heavy, and the quest has been programs never used so I can not say anything about them.