Not sure if it's the 'best' - that depends on your requirements: eg do you routinely need to illuminate the interior of a large concert hall, do you need high-speed sync, are you OK with manual flash control, do you have a certain $$ budget. Etc etc. From my own use, the Metz 52-AF1 works great for casual un-structured shooting.
But if need be my 30 year old Metz 45-CT1 works OK too, with a Cactus v6 wireless trigger driving it.
The flash area of this forum is probably the best place to ask about flash options.
Flashes, Lighting, and Studio - PentaxForums.com