It would be stupid for GB to trade the best WR on their team IMO. Its not like their offense showed much in week one. Without that punt return TD (which should have been called back on a penalty) they would have been embarrassed by the 49ers. And yes I think Jennings is better than Nelson.
EDIT: Then again... he is injured and may not play tonight (not sure on that though)... if they could get a first or second rounder it may be worth it. I think their best bet is to hold on to him though. He can is clearly a very good WR.