DB is the higher single target option since Fervor still has the limits of GCD capping you (yes, you get 100 focus, but you don't have the GCDs to effectively squeeze more AS off). ToTH is amazing for AoE.
ToTH isn't even that bad for single target. yes DB is better, bat as I only play SV on AoE fights, taking ToTH in the SV specc is kind of a no-brianer. (it's not that good on a multidot fight (non-multishot), not enough gcd's to get all the free AS off)
thanks to ToTH you will be using so few Kobras, and will be able to do ES, 3x AS, 1x Cobra rota a lot. (and no, if you take care, Serpent will not fall of. it does occasionally happen that a full stack of ToTH dropps off because of having so much to do, but happens very rarely)
Mathematically DB is better. But I play SV and in practice I much more prefer how many times a free AS and cheap (multi-)SrS comes in handy thanks to TotH.
Every fight has multiple moments where those TotH procs give you extra attacks during any part of the fight. Another thing is that with TotH you also have quick control on where you apply damage where DB is set-it-and-forget-it with possible downtime due to fight mechanics.
Even on single target fights it's beneficial. We did Tsulong first time yesterday and I found TotH extremely usefull. With constantly fishing ES procs and TotH, I still had to CS 2 or 3 times each day phase. Wich would have been many more if I went for DB with an extra pet that would never reach it's target before it died.
In the end the differences are small and that's one of the things Bliz did very well on hunters in MOP. Except for the T4 in my case, I've switched around all the other tier talents from fight to fight because each has their own strengths on certain fights. The only talents I haven't used yet are Narrow Escape and Powershot. NE I'll certainly use somewhere when we need aoe cc and Powershot just needs to be fixed so that it isn't a "skill shot" anymore.