Which pitcher(s) should I pick up?

Jordan Zimmerman, Ricky Romero, Fransisco Liriano, or Scott Richmond? I have a huge contrast between good pitching and mediocre. I have Lince, Halladay, Johan, and Edwin Jackson. Then I have Scherzer, Dempster, and Slowey. Romero has a 2.85 era, Zimmerman gets a lot of k's and has pitched great of late, Richmond is solid, and Liriano has a lot of upside, I'm just not sure what to do. I want to get rid of one of my pitchers or Chad Qualls because he has not been good. I have Nathan, Wilson, and Bailey as my other 3 closers. Also, since I have Ibanez coming back from the DL I will need to drop someone so I've been looking to do a 2 for 1 trade to keep my roster felxible.