That SE X1 looks really, really nice if you ask me. Seems like other mobile phone manufacturers are almost done with developing their own iphone-killers without cloning Apple too much.
The X1 has a keyboard as you can see below, where the m8 does not. The m8 has a slightly bigger screen, but SE has a "widescreen VGA" screen that consists out of 800x480 pixels which is better and sharper than that of the m8. It has 3G and 3,5G while the m8 has neither and runs Windows Mobile. On the downside there is only 400mb of free space on the device so you'll have to put an additional microsd card in for more space. Price wont be cheap.
The m8 is definetely outspecced by now, which is not surprising actually. The only point on which they compete right now is the cheap(er) price.
Watch the pictures below.