For fastest, Avast is a good choice, I'm using it at work, but gives way too many false positives, and is full of advertisements.
The best I know is Kaspersky, I use it at my desktop at home and goes really well, but is quite slow and a resource hog, however it catches may viruses and has a good detection ratio.
MSE is nice because it doesn't has any ads (because it's the only I know that doesn't has a paid version), but lacks in many aspects and is not something I would recommend to anyone. Quite fast too.
Personally, I would choose Kaspersky if you want to afford some money for it. Otherwise stick with the free Avast or Avira.