Expanding Expose’ to the Dock and Application Switcher feels like it should be a really welcome edition. But just recently I’ve started getting the Option-Tab key combo into my muscle memory. Expose’ is clearly the sexier of the two, but Witch’s basic functionality (pick from list of windows) may be more effective.
I think the key differentiator is that Witch has hysteresis across all open windows. The ones you’ve used most recently are near the top of the list. Expose only has the most recent applications in Least Recently Used order. If you’re going across windows in multiple apps a lot, there’s a little speed penalty. You need two navigations, first to the app and then within the app. For this task, minor speed deficits add up quick.
I think I’ll stick with Witch on this one.