Opinions vary. You can find/read plenty of threads about which combinations of antivirus and malware scanners people use - so there is no need to start yet another series of posts about that.
As far as performance: I use nothing. I let Windows do what it was written to do.
I might run CCleaner from time to time (not the registry cleaning part) but that does not improve performance or stability by any amount that I can see or even measure with benchmarking software.
Most important is to get and keep a perfect install, using the steps collected from helping with tens of thousands of installs here in Clean Reinstall - Factory OEM Windows 7 which are the same for retail.
As long as you stick with the tools and methods in the the tutorial, you'll maintain a perfect install for as long as you do.