Addai is probably the better pickup. You have to think the Colts will evolve into a run-first offense and that should at least give more touches for Addai. Clark unfortunately has been being used more as a blocker to protect Kerry Collins and I don't see that changing anytime soon.
Keep Jordy Nelson. He's emerging as a solid WR3/flex option.
14tm. PPR+IDP+return-yds. league
TE-Finley K & IDP-[streaming]