With Windows 8 NONE of these do anything extra whatsoever -- why bother with this stuff.
Please tell me what Malwarebytes has found that the built in Windows defender hasn't. As for AVAST (free) totally a waste of time these days.
Windows 8 has implemented security TOTALLY DIFFERENTLY to previous OS'es. Most of the security concerns I read on this section are 100% perfectly valid for WINDOWS 7 and previous OS'es and yes install all this stuff if you like - but even for Windows 7 Ms's own MSE is probably just as good (or bad) as all the rest of them.
Windows 8 is a TOTALLY new animal when it comes to security -- using a lot of these products is like applying a 20th century solution to a 21st century problem. SAVE YOUR MONEY.
Unless you are defending Corporate networks ALL 3rd party A/V software for Windows 8 is a WASTE of money if paid for these days --save your money and put it towards buying an SSD -- a much more useful purchase.
Incidentally ignore also any old comparative reports of effectiveness of A/V software -- these reports are always OUT OF DATE by the time you read them -- a new threat could potentially appear AT ANY TIME so analysis of last months (or usually longer ago than that) is about as useful as last months HORSE RACING results when thinking about what horse to choose for the 14.00 Exeter meet (or wherever).