Well heres a bit of a overview of what i experienced owning both of these cans..
Im a college student that commutes everyday to and from campus for at least 2hours a day so listening to good quality headphones/earphones off my ipod is an ongoing process with me.
These are some points i have just jotted down of each can for my situation.. not in any particular order, good and bad-
my recently purchased HD228's considering it only has roughly 20hrs burn-in (also taken out the centre oval pads):
Good solid bass, not blochy or distored. Also the hd228 sounds very balanced across the frequencies, lows does not seem to overpower the mids and highs.
Single side cord, found it makes big a difference in style and comfort (its not as annoying as having two cords on both sides). You would think this is a very minor aspect but commuting to and from college and walking for hours i have found it alot easier to manage.
Most hd228 owners would agree with me that these cans need to be placed at the right hieght and perfect angle on your head to produce its true capablilites, but once you get that angle it sits and holds its position very well on your head...i have a theory that the only reason why i see bad reviews about these is from owners with abnormally sized heads/ears that couldnt get the headphones sitting right lol. I have found sennheiser has always great ergonomics, and always fitted my head perfectly.
It takes a more power to drive than the px100's.. i had to turn up the volume a bit more to achieve the same loudness of the px100 cans.
Looks freekn awesome, gets complements often
Pads keep ur ears snug without making it too hot which is perfect in colder climate areas.. although in hotter areas it might not be very comfortable to have these on for too long
My px100 is at its prime you could say, it has had hundreds of hours of burn-in now
Very solid performing can, i have loved the sound produced from them the moment i got them! Realistic pure bass that is perfect balance with the mids and highs.
Open design means that it gets that clear undistorted sound, but also at the price of leakage.. personally i never cared if other people can hear and get annoyed to what im listening to because im never going to sacrifice my listening pleasures for complete strangers.. but leakage back into the can is the main issue for me. Commuting, talking and just general sound could easily get back into them, and at times i could even here what other people were listening to on their headphones over mine! Hearing the buses engine while playing my music is not something i wanna hear.
Personally i have never liked the styling on it.. reminds me too much of those headphones they supply you while on travelling on a plane.
Comparing their sound is like apples and oranges with the different open and closed styles. Although they are both great at producing clear punchy solid sound (when the hd228 has done the 'asteroid mod' to it). I cant stress enough the improvement it makes by removing the centre pads on the hd228's! It adds so much dimension to the can. Also i find it a lot more comfortable without the centre ovals..
Surprisingly when you take out the center pads its almost like an open headphone. Its very similar to that of the px100's but with a slightly darker feel to them
so the verdict,
I would recommend if you are using the can for home use or quietish surroundings and if you dont mind the styling then go with the px100's for sure. Easier to drive, easy to get the perfect position on your head, typically cheaper than the hd228's and i think produces slightly better sound experience when there is nothing going on around you.
Although if you are looking for a can that you want to take around college and/or you will have some kind of ambient noise then definitely the hd228's. Leakage is considerably less than the px100.. Your listening experience is not disturbed by other soundwaves and your music is more concerntrated to yourself. It also looks killer
And if you want the best of both worlds get both like me
.. oh yea heres a pic of them side by side to show the size difference..