AVG is not antispyware program....AVG is anti-virus program.
All anti spyware and anti-virus programs will slow your computer a little bit....the more protection you require the more intrusive and slower your computer will become...
I have used these programs for may years...
Avira....free anti-virus program...have to put up with an addvertisement page when updating everyday for the free version
Spybot S&D (free)
All of these ran regularly have been successful in keeping my systems clean and running fast.
Note: you can have the most expensive and best of everything but if you do not exercise self control over your internet browsing...they mean nothing at all!
1) If you do not know who an email is from....do not open it or any attachments at all...just delete it.
2) Do not allow any downloads from sites that you do not request first.
3) do not fall for the scams that you won something
4) do not give out any personal information to forums or blog and chat sites..especially your email address or create an email just for that purpose (once determined that they are not spamming you the email can be forwarded)