The Katadyne is one of the best in the world but it is also very expensive. If money is not a limiting factor then I would buy the Katadyn, however if you are on a budget then I would buy the MSR. I have both and used both - they both get the job done. Be sure if you buy the Katadyn you buy an extra element since they are ceramic and can break if dropped.
I've used the Katadyn Combi for many weeklong wilderness trips over the past four years. I wanted something durable and totally dependable that filtered water quickly, especially for times when I go on solo trips and my only backup is purification tablets. The Combi weighs about 5oz more than MiniWorks, however I think the Combi ceramic element has a larger surface area so it pumps faster and goes longer before pumping gets harder (and you need to scrub algae etc off the ceramic surface).
Even though the Combi weighs a bit more, I feel the "cleaner simpler" straight in-line pump shape is probably easier to fit in my pack, as opposed to the more irregular shape of the MiniWorks with the lever sticking out one side. Several times I wondered if I should get a lighter pump, but then I review all the options and decide I'm happiest with my beefy but fast and durable Combi.
The Combi has a straight in-line pump action as opposed to a lever action on the MiniWorks. If the combi is screwed onto the top of a rigid Nalgene or other bottle then you can brace the bottle on a rock and I think the straight-line pumping action of the Combi directly against the rock is easier and more convenient. There aren't a lot of screw threads on a Nalgene though, so sometimes it may come unscrewed from a bottle - probably an issue with any filter. Pumping into a 2 or 3 liter flexible bladder might be a tossup with the MiniWorks - I generally push the Combi braced against my thigh or a rock. I bought a 3rd party FirstNeed adapter to pump into the smaller openings on Platypus Platy 1-L bottles, which unfortunately were much harder to keep screwed on than standard wide-mouth Nalgenes (http://www.amazon.com/Platypus-PlusBottle-Holster-Black-Liter/dp/B0026P9418/ref=sr_1_11?ie=UTF8&qid=1381034264&sr=8-11&keywords=platypus+bottle).
Generally I'm filtering snowmelt at high altitudes in the mountains. However if I ever took my filter somewhere that pesticides or other chemicals are an issue, I like the fact the carbon filter in the Combi and MiniWorks will remove chemicals (and bad taste) that the ceramic element alone will not.
I borrowed a friend's MiniWorks a few times on a trip and among all the other options out there, MiniWorks would be my 2nd best choice after the Combi. I like the fact that ceramic filters can quickly and easily be scrubbed with a scouring pad in the field whenever algae or other tiny particles start to clog the tiny pores, unlike a throw-away filter. (Next time i go into the wilderness I'll try putting a coffee filter over the intake so this doesn't happen quite so quickly) Specs for ceramic filters show they are heavier ... but then consider that if you have to bring a spare disposable filter, then paper filters like the "lighter" HikerPro will probably weigh just as much and take as much space in your pack. Hope this helps others.