I had Avast free installed since a couple of month on one of my computer and this morning I decided to try OA free but after a couple of hours I got a BSOD. I did a reboot but as soon I try to open Chrome or Firefox, the computer crash again. Back to Comodo free
It is likely avast! is the cause. Avast! has a lot of BSOD problems. Try Outpost Free, it's very good.
I too confirm that OA & Avast sometimes don't work well together. The suggestion that you use OutPost free is really a good suggestion. It works well for me.
Stick with Comodo, it will be the best compatibility with avast. They have done a lot of work to make it good for use with different products.