Both look good.
The Wiz is by an established company that already did a bunch of machines (the many GP32 and GP2X revisions). The Pandora is the first machine of some guys who look like they know their stuff and are very open about what they're doing. The Pandora will however be twice as expensive (reaches the price of a netbook).
Me, I'll wait some reviews and see the developer community acceptance before making a move (the Wiz has a road paved as it just requires recompilation to use GP2X software - the Pandora might need changing code).
[download a life]