I'd have to say combofix has been the most effective. Malwarebytes catches most everything I've seen. However, there was one PC giving me some real fits. No matter what I did, no scanners were finding the infection. I ran superantispyware, malwarebytes, sophos, avast, avira, panda, spybot and ESET. None of them could find it.
Combofix was the only scanner that found and removed the rootkit. Combofix is a little different. It doesn't show you the results, and ask you what you want to do. It just does it. It's powerful, but effective.