I'm using Avira at present which is more compatible with Vista than AVG and Avast which I tried but Un-installed. Try it for Free and see what you think as it is unobtrusive.
I'm using AVG and its great, I used to have Norton and personally didn't like it very much. I used to have Avast as well which was ok. If I were you though I would probably get AVG.
AVG can have problems when installed on a Vista machine.I had used AVG for years and always advised people to use it,now I won't touch it with a barge pole!
I've never been keen on Avast either.I now use Avira and it is very good.
Norton is to be avoided like the plague unless you want it to take over your PC.
bottom line is none of us actually knows - "I like it" means nothing - if you don't visit sites that hve viruses - of course your package seems ok
(I got some giraffe spray the other week .... haven't seen a giraffe since)
the mags are reviewing virus protection this month - lurk tesco's mag rack and do a bit of reading
they test the packages - with a known list of live viruses - and compare the packages in a controlled way -
much more reliable than "I like the colour of the buttons"
the shop I bought my PC from put AVG on all their new PC's and reccomend it to anyone who brings in a PC for repair.
I have used it for years and have had no trouble, and I surf a lot for my part-time job.
I found Norton to be a royal pain, and the shop agreed with me - it is intrusive and blocks stuff you want as well as stuff you don't, which rather defeats the object.
I personally favour Kaspersky. Of the big 3 it requires the least resources and you can get a genuine 3 user licence on ebay for < �20. Of the freebies I have used AVG and Commodo and of the two I prefer Commodo.
No AV or firewall is foolproof. Internet use and emails still require due diligence by the user.