Both players have cheap build quality, but at about $100 each and the features they offer; I can live with that. The last DVD player I bought was $90 without any USB port or network features!
Samsung has a touch sensitive plate on the front and it is quite sensitive. I have turned off the player by mistake while attaching the USB drive which is right under the power button! Sony on the other hand went with really tiny, hard to find buttons on the front panel. Both models disappoint for their front panels. Both of them turn the TV ON automatically though - one button to press :)
Both have wireless ready functionality (which I don't care for) as well as a real network port. Connected network cable to each of them and after basic configuration both of them upgrade to the latest firmware. Upgrade of firmware over network was a breeze.
Interface: I prefer the Sony interface as it is similar to the PS3. Samsung has too many things on the same screen and too many colours. Sony interface design simply trumps Samsung.
As far as media playing is concerened: Sony just sucks as it won't understand anything except FAT-32 formatted media. Sony does note that in the fine-print, but hey we are in 2010 and if Samsung does not have any problem in reading content from NTFS formatted USB drive
There was one thing keeping me from returning the Sony but after finding out the media playing ability of the Samsung, there is no confusion.
Update: removed DLNA issue with Sony