^
I guess you read some misleading post. Most headsets are compatible with the Xperia S. Only the made for iphone headsets have some trouble. They don't function properly. Though you CAN use even the Made for Iphone headsets with a trick.
Just hold the + button on the headset in line controller while plugging it in the 3.5mm jack. Then you can use the earphones to listen to music though the mic won't function.
What headset do you plan to use ? And no there is no restriction that only Sony earphones will work. Any OMTP compatible earphone will work.
About the Mass Storage option, yes the phone doesn't have mass storage option but there is a MOD available to get it once you root the phone.
Data Transfers are blazing fast. I transferred a 1.8 GB file in about 3 minutes.
1 GB file shouldn't take more than 2 minutes. 100-200mb files are transferred in an instant almost.
As far as HTC One X goes, sure its a more powerful handset but it also has a whole lot of bugs. Just check out the One X forum on XDA and most of the threads are about people complaining about quality control and software issues. Also has some serious multitasking limitations which most owners are unhappy about.
Also Xperia S has a better camera and the screen is better too except for viewing angles.
Not to mention (almost!) bug free software.
Everything runs smooth and with ICS update it should only get better.
Battery life has also improved with the latest .73 update, 1 day of moderate- heavy usage is easily achievable.