I'll go with flash on this one brehs.
I'm not super up to date on any of this stuff, but from what im gathering in this thread, flash ftw. To the people saying supes could just blow up the earth, couldn't the flash start running back in time before the impact of whatever supes is using to do it? Ya know, since he can perceive things at an attosecond, or less than a second, whichever is more cannon; and basically keep doing it until he finds a way to stop him/kill him before it actually happens.
To the people saying he can't grab supes because of the strength difference, I'm gathering he wouldn't need to grab him, but only touch him, to phase through his body and instagib him, or phase some important part of his body off of him to cause serious injury/death.
To the people saying even if he goes back in time, he wouldn't know where to find kryptonite: Well I'm pretty sure at some point in his super hero career, himself or his league has had some form of contact with kryptonite, whether it be just seeing it being placed in a safety box of some sort, or just watching it be destroyed. So he could run back to that time In his memory and acquire it before it had been set aside/destroyed.
Fun thread BTW