Which AV is better? I’ve been using Microsoft Security Essentials but I keep hearing about Avast.
I use Avast. Not too demanding on resources as some other AV and is one of the best on false-positives. But I’ve always heard that Microsoft Security Essentials is pretty good so can’t tell which one i better 
Avast works wonders for slower computers as it´s not trigger happy with resource usage, it´s also as mentioned great with false possitives, gets updates most if not all days automagically but my favorite feature is that it closes the connection with a website if it detects foul play as opposed to just letting you know like several other do. My point is that avast´s main feature is that its more focused in preventing rather than curing unlike most other AVs I find this works extremely well but I´m sure others have other opinions.
I use MSE and I have never encountered a problem from anything ever.
I don’t use any anti-virus. Be smart and you don’t really need it.
My avast suddenly thought that all .php sites are hoaxes, all videos are foul play, and stopped me from downloading anything.
Then i got spyware, and avast started to protect it, by stopping me from deleting it. (Safe mode + Malwarebytes File Assassin got rid of that.)
Since then, i’ve used MSE. (MSE + Malwarebytes + Spybot S&D + Housecall + common sense)
I recently made the switch from MSE to avast, because I also kept hearing of it.
Avast does indeed offer more protection because it detects suspicious application behavior which helps against unknown malware. It’s one of the two only av tools offering this feature for free I think (the other one being AVG). It also offers more advanced features like hooking to your mail client to check incoming/outgoing mails or sandboxing for free.
However, I really liked MSE for being so simple and unobtrusive. I needed a while to configure Avast until I was happy with it. In the beginning Avast’s auto-sandboxing really annoyed me, since it wanted to run every application it didn’t have any reputation information for in it’s sandbox.
I also think if you’re careful and know what you’re doing, you don’t necessarily need those advanced features and MSE’s basic protection is enough. I guess it just depends if you really want those other extra features, they do offer more protection though.
I’ve used both, and never had problems with either. MSE is more unobtrusive as Charli said, and does most everything in the background. Avast seems to give you pop ups to tell you a lot more things by default. In that case it’s more your preference. But I’m quite careful when I browse anyway, so when it comes to what happens in case something does get detected, I can’t really speak to that. Antivirus for me is more of just a safety net. I’m usually pretty careful but I like to have it there just in case something somehow managed to get in. That’s why I prefer MSE - I have some peace of mind without something bothering me all the time.
One other thing is that you have to register to use Avast, which I don’t really mind, but some people might be paranoid about that. Also, neither program was ever put much of a load on my PC, but I’ve always had a fairly powerful rig for gaming, so I guess my experience isn’t very helpful there. 