Of the three, I have to say I preffer ObjectDock. While it doesn't have all the features of the others yet, it screems performance and then some. Considering that all three are in early stages of development, they may all end up the same, none beeing better than any other. For now, performance is what I'm looking for.
On features, I hope that Stardock won't stop with the current featureset. The performance and smoothness of the animations is important, but I would also like to see at least all the same features as the real OSX dock, and perhaps more features. It would be nice to have the option of dragging ObjectDock and sliding it along the edge, or moving it to another edge. It would also be nice for each icon to have a context menu. Another feature I'd like to see is the ability to configure multiple docks. For users with multiple screens, it would be handy to have multiple docks with different sets of icons.
Thanks for a great tool, Stardock.