You don't need to switch from unity if you render in daz, I'm talking about the render engine not the game engine (though perhaps unity game engine can also act as a render engine). The workflow for most VN's on this site will be rendering a jpg or png in a raytraced render engine like iray (built into daz studio) which is then used in the game engine (unity or ren'py) as a background image.
My recommendation, do a tiny project (one scene with the main features you will use like dialogue), try it out in unity and ren'py and see which you like best and what will work best for your game. My prediction is you will find you can do more in unity as it is a fully featured framework but ren'py will save a lot of time as it is specialised for VNs.