For me the appeal of kindle is portability, convenience & the superior e ink technology for prolonged reading. A LCD display can never match that. My eyes don't feel tired even after being on the kindle for hours. In fact on my last trip to Australia I literally finished 2 novels back to back.
As they say YMMV, I read law school text books (usual 400-600 pages) and law books (6000+ pages) on my iPads for hours on end.
What annoyed me about e-ink was turning pages, and the ones I tried a few years back where a bit low in resolution, but that might be a lot better these days. Ereaders are unbeaten kings of power-consumption. Or lack there of
When you get older, your eyes need more light, an kindle doesn't light up, so an iPad has advantages.
But my mother in law loves her ereader a lot as well.