Overland Journal had what I thought was a very good and thorough review of several different types of water treatment in their Fall 2009 issue. Sadly, I don't think it is available online. I think posting the whole article would be a forum no-no but I can find some way of getting it to you if others don't provide enough good info. Send me a PM if you're interested.
Doug Ritter of course has very good info elsewhere on this site.

In short, the Overland Journal tested 6 personal systems and 6 groups systems with E. Coli at 3 concentration levels as well as Enterocci:
Personal Systems
MSR Sweetwater (O.J.'s value award)
General Ecology First Need XL (O.J.'s Editor's Choice)
Steripen (A surprise disappointment but it may have been a testing issue)
MSR Miox
Lifesaver 4000
Katydyn Pocket Microfilter
Group Systems:
Cascade Designs Platypus Cleanstream Gravity Filter System
Katydyn Base Camp Microfilter
Katydyn Expedition (O.J.'s Editor's Choice)
General Ecology Seagull IV (also failed to remove some contaminants)
3M Filtrete (also failed to remove some contaminants)
Doulton Supercarb IP100SC
Also, the Katydyn Micropur Water Purifier Tablets are reviewed in a sidebar.