Of the pitchers, Colon is the one I'd go with. He's had an interesting year for sure. You may have to sit him for some games, but he has done well enoughto merit being rostered IMO.
As for Rasmus, I would grab him. Once the trade deadline has passed and he is moved or isn't moved, I suspect he might rebound. (I actually traded for him not too long ago in my league as a buy low for that reason. He may not be rostered now, but I sense a turnaround coming.)
Still, Colon will help you now, and hopefully for the ROS. Rasmus is a short term sleeper attempt as I see it. The upside, especially in the STL lineup however would tilt me to Rasmus if I were you.
David Hernadez is the one to drop regardless of the rest.
Thanks for the help on mine! Cheers!