Current Biglaw corporate associate - If you really want to do cap markets, Debevoise is probably the last big name firm I would go to for that in New York. They do have a varied issuers' side practice, but they have one notable client that is obscenely awful to work for (a large foreign conglomerate you've never heard of), and the deals take much longer than the average cap markets deal. There's a reason the midlevels in their cap markets group are laterals - they churn through associates in that securities practice, largely because of that client. The other work there isn't bad (I prefer issuer's side work overall to underwriter's side work, which is what most of Cravath's cap markets practice is), but that client is literally the single worst client I have heard about in the NY securities practice and you should run from there if you want to do cap markets (even just for a year). Otherwise, Deb's a good firm with good people, so if you want to do non-cap markets, there's no strong reason to pick one over the other.
Good luck with your decision. No matter where you end up, you'll be fine, so don't stress too much.
As an aside, I'm guessing 2006 mid-level associate market peak hours are probably not what a 2013 first year corp associate will work at any of those firms.