Having had both they each have their positives and negatives but are essentially the same thing assuming you go for AMD, the difference between E350 and E450 probably aren't work mentioning.
DM1
+ slightly better build quality, though not amazing, has lasted me longer than the x121 lasted.
+ better touch pad
+ better screen, x121 seemed to wash out at certain angles worse than the DM1
+ System status LED indicators on the machine like HDD activity, sorely missed from the x121
+ Sound out of this netbook is awesome considering its cheap ness.
+ I like the fact that the function keys are set such that access to F1 -F12 require you to press the function button and the other stuff like volume, brightness wiffi etc take priority.
- power hookup on left side quite annoying for me, particularly as its long and not angle, prefer the x121 rightside hookup (not a flaw as such more my circumstance, still it annoys)
- comes with 4Gb but 32bit OS, so you can access most of it but loose a few hundred MB, not really a bit deal but a bit of a fail in my book.
x121
+ Full ubuntu compatibility for basic AMD setup with no dicking about.
+ Win 7 x64 out of the box.
+ can get i3 in it if you need grunt over graphics.
+ better keyboard
+ better looking (subjective I suppose)
+ pointing nipple is awesome
+ some decent power save software that would light up only portions of the LCD that were in focus, course not so handy if you maximise every thing as I do, nice feature though.
- trackpad is awful with an annoying slope that makes things like double tap a difficulty.
- flimsy, I broke mine opening it by the screen, some flex my fault for sure but none of my other machines died in such a manner with same treatment.
- no LEDs to know what was going on when things started to crawl due to too much multitasking or background updates