three roads to quantum gravity by lee smolin or a new kind of science by stephen wolfram?
that would depend on what you want to learn from these books...
I'd say, go with Smolin. I don't much care for Wolfram, myself. But, then, that's just personal preference.
I, personally, went with Lee Smolin first. The book is highly enjoyable, but I advise taking your time while reading it, as it helps to understand it better.
Separate names with a comma.