So when I first looked at this I was like "Blah blah blah, Slayer with Cavalier features" and it didn't really jump out as anything special. On a second read-through though, I feel like maybe this archetype is actually really solid.
His Tactician ability is different than the standard Cavalier's in that while it does give him a bonus Teamwork feat, it doesn't actually tie his Tactician ability to that feat. Vanguard's Tactician can share any teamwork feat he knows, and he gets to choose between learning additional Slayer Talents or gaining additional uses of this ability. Considering how narrowly focused the Slayer Talents are, that makes it seem like this could be a really good trade, and potentially leave you with a Slayer who can have almost twice as many uses of Tactician as a Cavalier.
While this never drops below a standard action to use, it's pretty nicely complimented by his Vanguard's Bond which lets him share 1/2 his Studied Target bonus with all of his allies for a number of rounds equal to his INT mod as a move action, and his other abilities which trade Track and Stalker for 1/2 his level to initiative and the ability to always act in the surprise round.
So an archetype that's incentivized to pump his INT gives up some skill bonuses and two talents for a big initiative boost, a better version of Tactician than a Cavalier gets, the ability to buff his allies (granted a fairly mediocre buff, though Lenses of the Predator's Gaze can keep it pretty relevant in the PFS levels), and the ability to always act in the surprise round, potentially extremely valuable for a team leader character.
I'm thinking the Vanguard may have just replaced the Ranger as my favorite guild leader type of character. Has anyone else taken a look at this archetype, or have any thoughts on it?