I have both.
I have a pair of DX11s that I use to play CoD in my den (equivalent to the PX11 for Sony) and I have the PS3 Wireless Stereo Headset the I use to play PS3 and watch movies with late at night in my living room.
I like them both and for different reasons.
Wired-- no battery to replace or charge and no chance of wireless interference.
Dolby Headphone technology-- gives the absolute best positioning and surround sound experience when fed a Dolby Digital 5.1 source and is less fatiguing when listening to gunfire and explosions for hours on end.
Exceptional comfort-- the X11 headset is extremely lightweight and features oversized cloth pads that breathe better than leather allowing you to wear this headset for hours without discomfort.
Superb mic and chat controls-- mic quality is top notch and the simple two volume system of adjusting chat independent of game volume is a plus.
Flexibility-- works with anything with an audio out. (chat only works with Xbox 360/PS3 on the PX11)
Wired-- one cord with two connections to the DSS and another two from there to your console.
Dolby Headphone limitations-- works best when fed a Dolby Digital source, DTS and stereo up-mixed to surround not as impressive.
Lack of sound isolation-- the breathable ear cups don't do a very good job of keeping out noise OR keeping sound in.
Bass-- this might not be an issue on the PX11 version as it has a bass boost function but the DX11 has noticeably less bass than the Sony's. I think this has more to do with the ear cups not making a tight seal than the drivers themselves and either way I find too much bass while playing CoD to be distracting and exhausting.
Sony Wireless Stereo Headset pros:
Wireless-- oh man. Free at last, free at last, thank god allmighty I'm free at last! Wireless connectivity is convenient and consistent-- can wander my 1100 sq foot apt without a hint of break up or interference.
Rechargeable-- no AAAs to deal with, hours of life.
Virtual 7.1-- not nearly as good as Dolby Headphone but satisfying none the less.
Comfort and sound isolation-- the leather earcups do a fantastic job of keeping noise out and music in. The headset itself is very light for being wireless and I found it to be comfortable for several hours.
Bass-- if the headsets ah-rockin'...
Looks cool-- it really does. Your friends will be jealous... If they're nerds that is!
Price-- the price is a steal for what you get.
Sony Wireless Stereo Headset cons:
Recharging-- you have to plug them into a USB device and you're on your own for a cable.
Virtual 7.1 doesn't work with Bluray-- this may be my biggest gripe. Sure the surround mode is a glorified stereo widening and lacks the precision of Dolby Headphone... But why disable it for movie playback!? Ultimately it's more comfortable to listen to the virtual surround for extended periods as the sound is less 'in your head'. I really found I missed this feature about an hour into a movie...
Chat/game balance slider-- the headset features an Astro-like balance slider which allows you to modify the mix between chat and sound... It didn't work on the Astros and it doesn't work here. Separate volume controls FTW. Not a big deal as I rarely chat on PS3.
Long-term comfort-- let's be clear here that I've used these for hours at a time and have been perfectly happy... However... After a couple hours the combination of the added bulk for all that wireless gear and the zero breathability of the wonderfully sound isolating leather cushions begins to wear on me. I probably wouldn't even mention this if it wasn't for the fact that you can wear the X11s all day without even noticing they're on.
Proprietary-- these work with two sources: your PS3 and your PC.