I guess I should laid down some ground rules: completely featureless environment, no outside influences, they are at their best, and no killing (they ARE heroes).
The Flash would pummel Diana at near invisible speeds. With her nigh-invulnerability, she would be coherent enough to detect a pattern in his attacks. With her superspeed and cagey battle tactics, she would unleash a glancing blow to stun the Flash and finish the job. THEN she would collapse.
You mean Kingdom Come Flash? The multi-dimensional Flash that's pretty much everywhere, everytime? No, not him. The Flash in your thread looking sad and lonely. Not some alternate dimension wannabe.
By the white hair on my grandma's chin, when I said "at their best" I meant at their normal power levels, all rested up, and not suffering from any story elements that weaken them. (e.g. Flash broke his legs, Diana's blind) If you want to include KC Flash then I'll include Diana as a Greek Goddess. The result would be the same.
You're right though, Wonder Women if just fast enough to catch Flash with at least one blow, which is all she really needs with her strength. And, from what I've heard, she's already beaten Flash before.
Actually Wally is faster then ever, and he possess powers that no other Flash gain, i mean, this fight goes to him hands down.WW cannot approach too much high levels of speed cause Wonder Woman lacks the speed aura of true speedsters, the environmental effects/disruptions that she causes probably prevent her from utilizing superspeed mobility as a common mode of travel.And don't forget that Wally can arrive at lightspeed and enhance his physical mass at infinite level, and we all know what that kind of attack do.In a comic book, Diana would arrive at the Olympus with a punch like that.
WW's superspeed was granted by the gods. It's magical in nature. So Flash can not "disrupt" it as you described. The laws of physics does not apply to Diana. As for the infamous "infinity mass super punch" that the Flash used on the the Martian speedster, Zoom, it only occurred because the Martian was traveling at a high velocity like the Flash was. Flash compounding the excess energy created by the both of them to increase his mass and unleash it on Zoom. In other words, the Flash was absorbing the momentum from Zoom, combining it with his, exponentially increasing his mass, and releasing this energy at Zoom at the "end of the tunnel of photons" Diana isn't connected with the Speed Force. Her speed is magical in nature. She isn't capable of the speed seen in the first arc of the JLA. So there's no energy to absorb. Thus the Flash can't perform his ultimate attack.
Diana isn't stupid. She already knows that the Flash is much, much faster than her. So she won't even try to utlize her speed. With near-Superman strength and invulnerabilty, all she needs is one good hit. It's been done before. And yes, WW has kicked the Flash's ass before.
When the Flash reaches lightspeed, he cannot affect objects that are not moving at hyper-velocity. Zoom was affected because he was moving at hyper-velocity. There's some physics theory (no I don't know the exact wording, Mr. Bayha was a terrible teacher) that objects at light speed are immutable to their surrounding environments. In other words, they are intangible. The Flash has approached lightspeed to due his good deeds. But at lightspeed he can't affect anything because he's intangible. There have numerous writers who haven't taken this into consideration, but hey it's not a big deal. And this "infinity mass super punch" was only performed ONCE. Under the eyes of Grant Morrison. His name should say enough.