I have used the Steripen Classic, Aquamira, Katadyn Vario & Hiker Pro. I now use the MSR Hyperflow filter because no matter what conditions you face, you can always use it with proper care (don't drop it or let it freeze). Case in point: last weekend on Springer Mountain, Ga. the spring was almost dry. My buddy & I were able to filter out of a couple of inch deep pools that were the size of a salad plate. The Hyperflow filters from a surface floating pre-filter, is very fast (easy to deploy & put away), versatile with any water carrying system, compact(for a filter), & relatively lightweight, does not retain much water, & is field serviceable. It does require a "learning curve" to backflush it & to check for filter integrity.
I like the Hiker Pro filter(which also has worked in the above scenario), but like the lighter weight, compactness, & speed of the Hyperflow.