Lopez is behind Lyon, who blows. Soriano is behind Mariano, who does not blow. Both provide good peripherals (well, not counting Soriano's night last night), but I think Lyon could be next to lose his job, clearing way for Lopez. Skills being roughly equal, would you roll the dice and drop the guy behind the HOF'er for the guy behind the potential gas can?
No holds, just S, K, WHIP, ERA, where Lopez and Soriano are pretty similar (see below) albeit Soriano has much larger sample size and more K power and better OVERALL numbers....but their diff being that Lopez, I think, has a shorter path to (speculative) a full-time closer gig.
I've held off on Soriano myself because I don't see him getting saves. Yes, he'll give you some Ks and some innings, but no saves. Lopez gives you more of a shot in the long term.