Good opinions all, but I am inclined to disagree with the consensus.
In this situation I would trade Pennington for two reasons:
1)He is very hot right now and will probably get more for you than Hass will.
2)I would not want to be starting Penny come playoff time. The Jets schedule from here out is brutal. Whereas the Seattle schedule here out is an absolute cake-walk.
I would trade Penny for a top D. If your league is like mine then the Ds can be quite high scoring and can mean the difference between a win and a loss.
See if a team or two at the bottom of the ladder has one of the following Ds: Tennessee, St.Louis, Kansas City, Tampa, (not necessarily in that order)..
I would then consider carrying those two Ds throughout and play the matchups each week.
If you had a comfortable distance on the second place team I would say stand pat and go without a D this week, but it does not appear you have that luxury.
Good luck - with your team you shouldn't need it!!