Haste and Multistrike are the two best stats for Combat, so Witherbark's and Gor'ashan's are likely to be the two best default heroic choices (disregarding Skull of War)
The PPM rate on Witherbark's means you'll have on average a 15% up-time on the buff, which equates to a raw 207 haste, which makes it really good.
Assuming you use Gor'ashan's on cooldown, you'll have on average a 16% up time, which equates to a raw 170 multistrike.
Blood Seal is probably the worst of the ones you have so I would disregard that.
Kihra's grants 1060 of a stat (same as Gor'ashan's), but it's mastery, which is worse, and on a longer cooldown, so even with the socket I would disregard that too.
Skull of War has higher agility due to its higher item level which an obvious plus, and the proc works out at roughly a raw 223 crit. This makes it the best choice, slightly, out of the five you have linked (the difference between the secondary stats isn't massive, but the agility makes up for that), and would likely replace Gor'ashan's. Obviously though, this trinket will be very expensive and will be replaced in Highmaul once you obtain the trinkets from Butcher and Imperator, so for a minor increase you really have to consider whether you're happy to spend between 50 and 100k depending on your server, for something that will be permanently replaced within a couple of weeks