I must say, I'm rather evenly torn between the two... The biggest differences that I can see between the two are: Battery, camera, internal memory/processor, and shipped OS.
X10 has the larger battery capacity, though that doesn't
necessarily mean longer battery life... (this could be a big decision point for me).
X10 also has a more detailed camera, however I've come to notice that a higher number in MP section DOES NOT mean better camera. I'll instantly take the 5MP camera over the 8.1MP camera if the 8.1 takes too long to focus, is too sensitive to movement or just generally takes crappy pictures. (Also a potentially sticky area for me.)
Liquid has the more recent OS and being on Rogers I've all but determined that the safest bet might be to make the choice as things stand
now rather than how they
might be later. (As a for instance, the Dream is capable of "evolving" to Android 1.6... I don't think I need to elaborate any further.
)
As for the memory differences, I honestly don't think that I would ever notice a difference. As long as the processors are capable of handling the OS that ships with the phone (within reasonable limits), I'm not likely to press the processors much further than that, so I can't see that it would be an issue for me.
As it stands, my personal preference lies with the X10, but that has mostly to do with looks. Both of the phone itself, and what I've seen of Sony's OS. Otherwise, I'm almost perfectly on the fence about the two.