>>402549585
I haven't used Waifu diffusion much but I really feel like NovelAi blows it out the water. It really seems like high strenght tend to be so much more reliable. 
It can give you so many different results with just the same prompt. The ease of use is a welcome plus.
You still gotta be patient with your prompt and fiddle with the settings, It's not perfect of course but I feel like it fills the missing gaps much better.
I'm not sure if I'd recommend it just for image generation, I already had a sub to NovelAi since I enjoy using it as a writing tool.