i have 2 pairs of KSC-35, and have had the PortaPro and PX100.
the KSC-35 i think are the most comfortable, because they are lighter, and kinda hangs off your ear rather than press pressure on them. Their sound is really balanced, but not as 'impactful' as is the PX200. Their build quality totally sucks, the cord is slightly too long for portable use, and they dont have a cord clip thingy so the left and right channel cord falls down to your belly
the PortaPro is a bit more bass heavy than the KSC-35, but it can be described as somewhat bloated. theyre a bit louder than the ksc-35 (because of the positioning on your ears, probably). they are comfortable, but not as portable to carry as the sennheier PX-xxx (they fold but not as well)
the PX100 i think was the worst of the bunch. total duds. their sound is warm and dull. just...overly warm... not exciting
the PX200 is a gem. the sound is really clear, and the bass is solid. they are very impactful and strong. they fold up neatly for sticking in your pocket, and the case really protects it well.
alot of people either love the px100 and hate the px200 or visa-versa... i tended to the px200.
open headphones are, generally, better than closed headphones because they provide a wider and more natural stage. however i find the px200 to do exceptionally well in all areas, though