I've ridden, race bike wise
trek ex 8
the fastest feeling has to be the spark, but it has a very low bottom bracket, great for cornering but rubbish for anything technical ascending wise, especially as its single pivot.
The Anthem is very involving, and gives you a false sense of speed. its quick, but not as quick as it feels.
I've not spent enough time on the flux to give good comment, but it has the most traction of any bike I've ridden ascending, and descends like a 140mm bike. it feels as if the whole bike compresses, not just the back end.
I've yet to ride a Yeti, knowing me ill have one at some point though.
I did look at an asr5, but I really don't want another carbon bike, even if its just the backend. its comfy, yes, but is prefer not to worry about falling off and cracking the frame or swingarm.