No doubt e-ink better. E-ink here being the broad term for reflective display techs, not the particular one from one company, and should also count TFT LCD and Mirasol displays among them.
That said, I don't care. I won't be reading under the sun so that backlit becomes inviable, but then neither will be Kindle users: you can see from the iconic image they too prefer to read under a tree's shadow. Indeed or on the bed too, where having backlight is an advantage (as long as I can dim it).
The only eyestrain I feel occasionally is when I'm reading on the bus and there's too much trepidation. It's got nothing to do with display tech, only the fact that it makes harder for the eyes to follow the smaller font. In those moments, I simply put aside reading and wait for more stable terrain.
