Problems with Avast anti-virus.

I have downloaded Avast Anti-virus  for trial use and been using it for a couple of days,now,but  I have several problems as follows:

1. Downloading of YouTube is pretty slow & lagging.  It takes about a few minutes until it  gets started off.

2.  Some of my favorite websites cannot be accessed but most of them I  can do it..

 For your info. before this I had used Avira and didn't have any problems at all.  I would appreciate any clarification on these problems which may lead me to my decision whether I should go ahead  to buying Avast program

Than you.