Kaspersky heard next F-Secure and Norton to the manufacturers whose products, at least in recent years on my PC (Windows XP, Vista and Win7x64) worked very well. The performance loss is acceptable, and only in some cases there were difficulties with existing configurations. If you look at the test results of large test portals look are currently Kaspersky, F-Secure and Bidefender of their protective effect "up front". If you still a little look around in the user forums, Bitdefender may seem an excellent scanner but to have a bumpy stability. The two well-known products from Germany, I personally (I really do not want to generalize) bad experiences - to finally ensure the support for 64bit systems completely until today problems with performance through the two parallel scanner and the inability of the other manufacturer.
So stay in the moment for me only Kaspersky and F-Secure. At the moment I use Kasperkys Internet Security 2012. What I find remarkable about Kasperkys software is really impressive variety of detailed settings. And if a man is engaged in the program, it can adapt very nice. The possibility under a 64bit operating system to launch programs in a sandbox foreclosed hardly has a rival.
The launch of Windows, however, takes a comparatively long time. Starting and unzip downloaded program files is also pretty thwarted by the virus monitor. Of course you can just here to fine-tune what depth of heuristics, etc. are concerned. Nevertheless, the performance loss is acceptable and overall the software is stable and reliable.
Although Kaspersky offers numerous setting options, you can work very well with the default settings - seems at least to me this fact to be very well adjusted. And yet not a single false alarm!