I have been an AVG user for the past four or five years, and have found it to be exemplary in all regards.
Of course, you must understand that I had used Norton in the past, and (I am embarrassed to admit this) I even tried McAfee once because it came bundled free with some tax preparation software. After the
nightmare of trying to purge McAfee from my computer (AVG now offers a free utility for doing that) I tried AVG and never looked back.
AVG turned out to be so unobtrusive and transparent (compared to Norton that takes over your whole computer, and McAfee that clings tenaciously despite every reasonable effort to remove it) that I upgraded from the free version to the "Pro" version, not because the Pro version offered anything I needed but because I was so grateful to them for getting me out of the hands of Norton and McAfee.
I am currently running AVG 9.0.664 and have
not found it to be slow, big, intrusive, or any of the other bad things that people here have said. Of course, you have to remember what my basis for comparison is!
Do you remember back in the DOS and early Windows 3.x days when Norton Utilities was Peter Norton himself, and the package was a delightful and useful group of little standalone utilities that nobody who was comfortable with a C:> prompt could live without? Ahhh, the Good Old Days. I still say this whole Windows and GUI business is just a passing fad, and any day now we'll be back to C:> prompts and command line computing.

tanstaafl.