that people use .tk domains for viruses are all plain lies, it's a normal domain nd makes no difference to .com, .org , etc. It's a "name" of the websites actual Ip.
none of these wins imo since nothing makes one of them better than the other. co.cc etc are often used for runescape ,wow , etc clan sites though. By some reason I notice alot of phsining sites on .tks though, I have no idea why people would make it .tk since nowaday many people recognizes .tk as suspicious...