i want to ask about Kaspersky AV 2010 , it's really making my pc too slow !
( i didn't want to purchase the 2011 or higher version cause i heard it will make the pc even slower ! )
i have Malwarebyte's installed too , can it replace the protection given by KS AV ?
if it doesn't , what's the best choice of anti-viruses ?
Malwarebytes is an on demand scanner, not a real time scanner. It's great for scanning when you think you may have an infection. However, it's not meant to stop infections.
Personally, I recommend using Avast free edition. It will provide real time protection for your PC, and is extremely light on resources.