I have used the pre-mac swp and mwp and premac state that the swp will work for 50 litres and the mwp will work for 400 litres and in the long term they work out quite expensive, but they do have plus sides to them, one being that you cannot fail to add a chemical purifier to your water.
I have used the Pur explorer (older model) which is basically a larger version of the pre-mac two stage purifier, it does have a far better flow rate than the pre-mac.
I have a Katadyn mini, they are very good, the flow rate isn't brilliant but acceptable, and they are possibly the best pocket filter on the market for size and weight, however you may still require to chemically sterilise the water that comes out of the filter. It does give you the option of adding strong poisons to your water and does not do it automatically like the pre-mac systems.
As far as being robust, easy to carry and tried and tested the millbank bag is a star. If you drop one it will not break, it will adopt most any shape of anywhere you wish to pack it and it doesn't get harder to pump as the filter gets more knackered. They are compact and once you have added whatever chemical that you are going to add to the water that has been through one it will be as good as any pre-mac going. They also have cost on thier side.
The pre-mac SWP will do 50 litres and costs £20, the Katadyn mini will filter 5,000 litres and cost £60. The millbank bag will cost £15 will filter thousands of litres of water and comes with a little pot of chemicals which you will have to replace every now and again at the cost of about £2.