The best TTL external flash I have tried so far with my new Sony A6300 is small and lightweight, but much more powerful than the built-in flash.
The Opteka IF-500 AF Speedlight is a lightweight and small on-camera flash that is compatible with most Sony E-Mount digital cameras featuring TTL support including the new Sony A6300 camera.
The external flash has a guide number of 130′ at ISO 100 and 105mm, this add-on camera flash can easily brighten up a room or subject. The Opteka IF-500 gives you a proper exposure and color balance with TTL metering for the A6300. Aside from TTL, you can use full manual control option to set output from 1/1 to 1/128 power. Weighing under 7.0 ozs, its small design makes traveling with this flash easy. The IF-500 is powered by two AA batteries which will provide a recycle time between .2 and 6 seconds depending on flash strength.
You can find the Opteka IF-500 AF Speedlight for the Sony a6300 with or without battery kit on the cheap.