Interestingly, the number of save opportunity a closer gets doesn't depend all that heavily on how good his team is. No, Yan isn't the greatest closer ever, but at the moment, I'll take him over guys like Looper, Julio or Gagne, even though they might have higher potential. Anyway, Yan's potential isn't low either - his stuff is nasty when he's on. Looper has potential too, but until he throws more strikeouts, I don't see him as a stud closer.
Escobar is another matter - he has great stuff as well, and has much fewer question marks than Looper. I'd call it a toss-up between Yan and Escobar.