Solid rejection on the other trade. As far as Jennings for Hanson, it is very close. Lester and Hamels is a solid start to a staff, but does Jennings possible 40 steals pose a bigger need for your team. Jennings will play great defense, steal some bases, and have a pretty good OBP, but his average and power will leave some to be desired. Which brings the question, who are the rest of your keepers.
Yeah we'd need to know the keeper structure and the rest of your keepers. League settings wouldn't hurt either. Jennings would be more valuable in an OBP league, I'd guess.
All things being equal I'd rather keep Jennings. Hitting > pitching, especially pitching with health questions. Even if you "plenty" of OF, in a league with the right keeper structure Jennings is a big trade chip. Chances are you can address a different need, preferably snagging a young, talented hitter. Ackley or Lawrie - someone whose position you don't have "plenty" of.
As much as I like Hanson, I think you need to keep Jennings here. Right now I think Jennings is over-rated and would look to move him but Hanson hasn't shown to be healthy enough.
"In the beginning the Universe was created. This has made a lot of people very angry and has been widely regarded as a bad move."- Douglas Adams
Seems to be getting redundant here, but I'm also in favor of Jennings over Hanson. If you want a SP, you can do better than Hansen, whose stock has certainly fallen since the injury.