Everyone has their own preference when it comes to flash exposure. If you prefer to work in TTL, honestly, I'd shoot Nikon. Pentax's pTTL system is still about 10 years behind the game. Maybe that will change with the K-1, but I would be astonished, and there has been no mention of a major revision.
If you like/(don't mind) working with manual flash though, the Cactus V6 system, with or without the companion RF60 flash guns, is a very nice workaround for Pentax shooter. (It's nice for shooters of all brands, but it addresses the shortcoming of the Pentax system almost as if it were purpose-built for the task). Most notably, it adds 4 "zones" or "groups" so that lighting ratios can be controlled from the camera by the user. It also has a pseudo-HSS mode, remote shutter triggering, and it's brand agnostic. You can learn more than you ever wanted to know in this thread:
https://www.pentaxforums.com/forums/125-flashes-lighting-studio/258624-cactus...er-review.html