Both of these phones have two cameras on the back, but they don't work like most other "dual camera" phones on the market. Instead of one featuring a zoom lens like Samsung or Apple, LG's secondary camera takes wide-angle photos. On both the G6 and V30.
With the V30 you get one 16 Megapixel camera with a fast f/1.6 aperture for fast focus and great low light photography. The G6's main camera is only 13MP and f/1.8 aperture.
The second lens is 13MP on both and features that wide-angle lens we mentioned earlier. Allowing owners to zoom out (essentially) for nice landscape photos or big family portraits. Basically getting more in the frame.
Based on that info the LG V30 camera is the clear winner, but we'll need to try it out for ourselves. Either way, both phones have pretty capable camera setups.