I have used all the major ones in the past.
Norton = Puts it's filthy claws into the entire O/S, when run at default it eats up resources like a whore on crack.
McAfee = Same as above but almost impossible to remove without killing your O/S or affecting it.
Ontrack = Lets you configure how much or how little of the software suite you want to install, during the install. Default installation uses very few resources (small footprint). Ontrack updates 2-4 times per week for the virus and trojans database (the others are less).
The winner = Ontrack! (by far)
Overall outlook = As for being able to find the most viruses and trojans, I would say Norton is best (maybe +1 or +2 out of 100 list). As for McAfee.... I would rather see no one use this pig. Ontrack is my favorite because it allows me to still be the boss

I like software that "I" control rather then "it" controls me! You might have noticed I have concentrated of the Anti-Virus aspect of it, this is because all the other features are more or less "bells and whistles." I would however, never recommend you use any form of "Crash-Proof."