Comodo Anti Virus

I just installed Comodo AntiVirus (not firewall) yesterday after using PC Tools AV for a couple of years. When I run a full system scan with Comodo, nothing else will work on my computer (windows 7 64bit). If I try to open a browser window or even task manager while the Comodo scan is running, it greys out and stops responding (the secondary apps I try to run do this, but Comodo keeps scanning). Is this normal for Comodo ? With PCTools, I can run a full system scan as part of my weekly/monthly maintenance and am still able to do other things on the computer while the scan is running. I really do not like the fact that I am unable to do anything at all while comodo is running. I was really just looking for a change from PCTools. It scans about 700gigs of used HD space (1 full 40gig SSD, and 2 partially full standard HD's) in about 15 minutes. Comodo was taking FAR longer than this.

#1: Is this normal behaviour for Comodo ?
#2: How is Avast! these days ? I used to use it, but it was very slow .
#3: Is PCTools AV, in your opinion, a good AV ? Maybe I should just go back to using it .

Thanks !

 

New Avast installed. Boy has Avast changed since I used it years ago ! Tons more customization. I can also now do other things while scanning system. I don't particularly care for or need the website rating tab thingy it slapped on my browser, but I'm sure I can get rid of that in the settings somewhere. Guess I'll ride with this for a while and see how I like it . . It doesn't appear to use much CPU or slow things down so . .. .