EDIT do what Tashi says
"best tool" depends on what the malware is

Do you know what your next infection will ber?

let me know and I'll suggest the best tool
Spybot Immunize, SD Helper and T-timer are excellent tools
The Malware Bytes Forum recommends Spybot as a valuable scanner as do many other professional sites.
A good Anti Virus like Avast
and a good third party firewall are essential
If you run Internet Explorer something to block Active X malware
a Hosts file
lots of things to consider
have you run Secunia software inspector?
If you think that you are currently infected
I suggest you go to the malware removal forum
read the stickies at the top and let them help you there