I may be the only one here who hates Norton, but oh well. I've used Norton once in awhile from back in DOS days and up to current (or almost current) and just never liked it. It also tends to not always release perfect virus definitions... about every other one, it will either state that the Invision script has a virus or doesn't. They can't make up their minds.
Anyhow, it's really just a personal preference other than the issues with Invision.

I actually do like McAfee and it really does do a great job. I won't say it's better than Norton because I've never tried to compare the two with different virii. However, it has been very rare (only a couple times) in all the years of using McAfee (again, since DOS days) that I've ever gotten a virus. And, when I did, it removed it without a fuss.
I have also tested McAfee now and then by purposely visiting sites known to try infecting you with virii. I even use IE to do so. And, even when I purposely go to these sites to test it, nothing gets through. So, I'd say it works quite well.
Regardless what AV you use, I do recommend running SpyBot Search & Destroy and Ad-Aware regularly just in case. And, if you use IE, you may want to also run Hijackthis now and then. The thing to remember with running these is that they CAN pick up legitimate files in their scans. Making changes to these files can cause the programs associated with the files to stop working. So, always check the path to the file they mention and the information about it to know if it really should be removed/repaired.
Also, I recently found a specified virus scanner that can be useful if you have specific types of virii and trojans and hijackers. It works great for removing the specific ones that it handles. It offers a fully working trial for 5-7 days, so if you know you have a virus that it can fix, you can use it to clean the virus. The program is Ad-Away. I found it by trying to help someone clean the About:Blank virus from their computer. Even the manual cleaning methods recommended weren't working, but this did it right away without a problem.