I'd rather Hoover wins the job due to the better ratios I think he'll give. So I think there's more upside there. However I honestly could see them going with Broxton since he's got experience, saves make guys like Hoover expensive, and they have a top closer that should come back by the all-star break. If they had a mediocre guy or if it was a shoulder that has serious risk of keeping him out all year I think they'd give Hoover a shot, but it wouldn't surprise me at all if Broxton got the first shot.
I'd pick up both if I had room. If I only had room for one, it would depend on my league. If closers and most next-in-line types are valued pretty highly in my (deep) league I might take Broxton since I think he's likely to get the first crack at saves, but it'd be close. If there's a couple lower-tier closers or at least the top next-in-line types laying around I'd want to take the upside guy and definitely grab Hoover.