I think semi 1 it's the most interesting. Bolt is going to be "challenged" by the NCAA products, Chinese Su is near sub 10 again, and Lemaitre always finds a way to be in the mix.
Semi 2: have two clear favourites in Gatlin and Rodgers, but don't sleep with Ashmeade and Ogunode.
Semi 3: I'm curious to see Vicaut's start. If he makes a good early phase, Gay could be in trouble. Asafa shouldn't be worried if he run sub 9.90 but we know how it's with Asafa and the pressure, so we'll see.