I think Lopez is a better option. Biddle and Graves most expect to lose the job to Chad Cordero and Josh Wagner. Either of them would be a great sleeper closer pick, Wagner probably being the better option.
Wickman is coming off injury, and also could lose the job to Riske, who is probably a better option. Wickman, Biddle, and Graves I just see getting lit up, their ERA's and WHIP being killers, and probably only a handful of saves for your trouble. You may HAVE to gamble on one regardless.
Lopez hasn't even officially gotten the job, but he looks like he should get it, and being closer for the Jays could produce decent save chances this year. His ERA and WHIP last year suggest he could be a pretty solid closer.
Joe Nathan I would think would be long gone, but if he is there he would be the best option. I like Lopez, I think he is your best option, but you should probably have 3 closers, maybe 4 on your squad. Not that you'd keep them all, but if Wickman, Graves or Biddle does hold the job and is halfway decent they are worth owning.
I'd say go for 2, but take a shot on Lopez for sure.
* Steroid induced record