Haven't tried Wiip yet, just Chiip and OpenWii. And for now, i'm sticking to Chiip. Less arogance in the team/creator, more media-compatibility.
Actually, both have about the same featureset right now. Just try all three and decide which one you like

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The Chiip's where it's at. I love this thing. It does it all that the commercial chips do. The programmer is easy enough to make.