I have never had as good of luck with shooting Av as I do Tv. When I shoot AV, if I have it at wide aperture, and the light is nice and bright, it puts my shutter speed upwards to 1/8000. And when it gets that high, the image actually turns out way too dark even though there is plenty of light. (It took me weeks to figure out the problem, I had posted examples of several boards until someone finally figured it out I believe I posted it here as well). I haven't had that problem with the 20D because the SS doesn't go that high, but with the MKII it always happens, on bright days with wide aperture when shooting AV. I have also had more consistant exposures on the images using TV than using AV.

Another reason I use TV is at times I'd rather have a slightly too dark image and have stopped action, then I can lighten it in photoshop, if using AV I might have a better exposure right out of the camera but blur that can't be corrected.

I wonder if the difference might partly be because I live where it is often cloudy so the ss is more of an issue...I would prefer shooting AV so I can control the exposure but maybe I am still not quite getting something as I get more keepers (over 90%) using TV and not that many using AV (when the light is either variable or low. I do get at least that many keepers with AV if the light is brighter and consistant but then I try to shoot around f/8 for the lens sweet spot and to not have the shutter speed super high to where it creates those dark images)