Most Important Feature in an eReader

If I had to choose just one feature as the most important in an eReader . . .

Would it be a logically and thoughtfully designed interface? Or ease of purchase (aka Project Don't Make Jana Get Out of Bed)? Or a large quantity of available content? Or price? All of these matter to me.

But I'm going to have to go with a logically and thoughtfully designed interface. I keep trying to give my Kindle (v1) a try, but the clunkiness of the object itself combined with the rotten navigation scheme keep sending me back to my iPod Touch.

Of course, having "the whole B&N ebook catalog at my fingertips" wouldn't hurt, either.

This post is part of a contest through BBAW (sponsored by IREX) to win an IREX eReader.