Guild Wars 2

Is there a weapon combo that that boost kits the most out over the other weapon, Rifle, Pistol & Pistol or Pistol & Shield?

As i understand it kits get some bonuses from your stats and weapons now but im not entirely sure on how that works.

Is there a specific stats or so that increase the kits power?

Yes there is. Using two weapons instead of one.
Reason: Two weapons → two sigils that your kits benefit on.

You may read the December 14 Update notes in News/Announcements for clarification.