Having tried both touch and button-style ebooks
I'm coming down strongly on the side of the buttons. Touch screens are all very well, but they are difficult to use one-handed (e.g. reading in bed) and you can't just pick the thing up and carry it with a bundle of other things without putting it to sleep first, lest you discover yourself six pages from where you thought you were.
It's possible that other interfaces work better - for example, browsing - but it's not something I do, so I can't comment. Though I do notice that on my Kobo touch, my fingers are often too dry to operate the touch screen.
Hmm. At least they're cheap enough now that you can by them on a whim.