Personally, I have both Atlas and Peco flex track. Forgetting whether one is European and the other US type track which, in my opinion, is irrelevant when it comes to over all quality. Comparing them side by side, the look, feel and functionality of the Peco Track is much better.
That being said, thee will always be "better" track, and Epimethius is probably right, Micro Engineering track is possibly better than both Peco and Atlas.
As for the turnouts, Peco has Atlas beaten hands down.
I may not be an expert, or even greatly experienced in track, but I also don't spend a squillian dollars on Atlas track just to rip it up and replace it with Peco Track for no reason.