i think nadia will win. she's so tough mentally, and taking out an in form jenn on clay is probably more difficult that taking out an out of form venus. also, nadia used to double bagel vera when they were very little. however, vera has risen more quickly... so it's still tough to call.
i already posted my opinion, but i just have to say that no matter who wins, i think it will be very long and emotional. no one will win easily. vera gives trouble to anyone she plays, and so does nadia. neither will take this one easily.
Nadia will win if she keeps her head together. Sometimes she is such a headcase, like a few weeks ago when she took the first set off Eleni 6-1 then she fell apart. Hopefully she will win this though, she needs the win more than Vera.