ITT: We miss the point.
There is no difference between the DSi LL and the DSi other than its size. The point of the 4.2 inch screen on the DSi LL is so that people with vision impairments (or the elderly) can play the DS without straining their eyes. The resolutions on both screens has not changed, and so DSi LL will have a lower pixel density and thus look a bit shittier. For us normal people, it is in no way preferable to regular DSi.
p.s. I knew Roph would make a thread about this when I read about it earlier.