i'm also going to buy a player soon and have decided it's going to be either the cowon j3 or the sony X. I haven't chose yet because 1) i don't know how's the interface and touch responsiveness of both, 2) sony's lack of sd slot, 3) for what i've read the sony doesn't need that much EQ tweaking compared to the cowon, and i don't know if i want to spend much time equalizing every time i use the player, i like plug n play. These are the main reasons, things like wifi, video(this i don't really know, it will be my first pmp) i don't care much.
I have yet to see pictures of both, but judging from the dimensions they seem to have similar size