My favorite is NOD32. Another good AV is Kaspersky, Zone Alarm uses their engine now and it's very good. I personally like NOD32 better because it just seems to suit me better and if something ain't broke don't fix it
I do like to test other AV's on my virtual machine. McAfee is awful IMO and I agree with DJ-CHRIS on that one. I used to use it a long time ago when I was new with computers and it always managed to crash my system and let stuff in that I didn't want in there like trojans and such.
Anyway here are the AV's I've tried and what I thought of them:
I tried the free edition. It's very good for a free program. If you want a simple, low resource AV with good protection this one might be right for you.
Avira Personal Edition Classic:
This is the free edition. I like it, it has great detection and it does very well in AV comparison tests. The only thing I don't like is the pop up window but I think it's worth it for the protection it offers. Also the "Luke Filewalker" is a cool name for it's scanning.
Avast! Home Edition:
Not bad, it's saved my parent's computer and does a good job of protecting with all of its shields. It is slightly heavier on RAM than the other two listed above but it's a good free program and the extra RAM usage is well worth it. The skins are pretty cool too.
I've heard this program uses the Kaspersky engine. It's good at detecting stuff but it's very RAM hungry. They do have a great online scanner that you can use for free though.
One of the worst AVs I've ever used. The updates didn't work half the time because their servers were down, and it didn't detect even obvious threats. Maybe I just wound up with bad luck, I don't know but I'm not trying this program again.
It's free, open source, and no nonsense. I use it as a backup scanner and it's never failed me yet! Also there's a free portable version for it that you can run on flash drives.
I like this program because it's awesome at detecting threats. Their research lab is regarded as one of the top in the world. The interface is also very easy to use. This is one of my favorites behind NOD32. If you want detection that's good, but want an easier to use interface than NOD32 then go with Kaspersky.
Seems kinda bloated and doesn't detect well. I've had too many bad experiences with McAfee so I won't use them anymore.
My personal favorite. It has saved my PC many times and uses low resources while keeping my PC safe. The only con is the interface isn't exactly user friendly but once you get the hang of it you'll be fine.
It was alright when I first got it, but it messed with my registry and caused my system to crash. Also their update method is rather strange and tech. support is awful. It's also a bit bloated.
Trend Micro PC-Cillin:
A bit bloated for me and when I tried it, I had issues getting it to install. It also wouldn't quarantine or delete the threats it found. Maybe it was just bad luck, I don't know.
They've gotten better since they got rid of the CA engine and switched to Kaspersky. Now it does a good job of detecting and removing threats.
It's all up to the person and what their personal preference is. There's no FACT saying that one AV is crap and the other is the best in the world. Just go with something you think gets the job done and does what you want it to do.
EDIT: Sorry for such a long post