I used Avast just ONCE 3 or 4 years ago. I put ZA on there as well, the two of them fought it out like cats and dogs and screwed up the PC something awful. By experience with Avast started on a bad note, I haven't used them since. But I don't badmouth them, don't "hate" them.
I hate Symantect because 50% of my work is figuring out how to fix/remove/install their garbage. Their bloatware that takes 15 startups and services to run, with inevitably at least 1 or 2 never working anyway. Their GoBack CRAP that screws up the hard drive boot sector.
The ONLY product I care for from them is their DOS based Ghost program. Which comes in handy sometimes. And occasionally I run WinDoctor directly from the CD to fix registry issues and ActiveX problems. Other then that, stay away!
I like AVG and also use it when retail AVs don't work. But I don't think it's as good as some like to think arount here, I just don't think it's very powerful and finds as much. And I've had a lot of issues with their update system.
I currently use Panda products, and Kaspersky Beta. I am happy with both (when they work). But Panda's issues have been increasing. I think Panda is very strong in detection and removal, but not very smooth in the registration, renewal, installing, department. Plus you get no phone tech support.
So I think my AV of choice right now is Kaspersky. It takes far less resources then Panda and far far less then Symantec.
Check out this thread about AVs:
https://www.techspot.com/vb/topic37621.html