For me it depends on the source. I've used one for over 15 years in the Sierra's and have never been sick, my first one was when they were still under the PUR name. I just got the hiker pro two weeks ago for an earthquake kit specifically because I have faith in them, from a mechanical aspect.
There are smaller filters and more efficient filters out there but this gets the giardia out which is the primary concern where I live and I've never had it fail, so I put a lot of value in it. I have broken one once but that was user error, fell canyoneering and it took out my slr camera at the same time. I've added Iodine and Chlorine (sperate occasions, not at the same time) to kill viruses if I'm pumping from questionable sources, namely stagnant water or obviously contaminated water. A steripen would work well too as another level of protection post-filter. In general I try to only pump from clear, swiftly moving sources.
The gravity fed filters are a very attractive option if you haven't already checked them out.