>>4751
Either works, but if you've got a powerful enough graphics card, i.e. a 30XX and upward, it's best to download Stable Diffusion Forge and a model of your preference (popular ones right now in the meta are Illustrious and NoobAI) and generate pictures natively from your computer. NovelAI is very good too, but it's subscription-based, which costs money, 25$ to be precise. Not very much, but if you have the option to generate pictures for free, you may as well choose to do that. NovelAI is also less flexible than Stable Diffusion overall, but it's robust enough to do what you need right now if you choose to use it. It's two different workflows, though. I find NovelAI easier and quicker than Stable Diffusion (though SD's speed depends on your computer's power), while Stable Diffusion allows for more creative freedom. I started out with genning with NovelAI, back in V1, in 2022. It's very straightforward. Put your prompt in, do some minimal setting adjustments (there aren't many settings you can tweak) and generate. Then inpaint, upscale, edit, draw on the picture, regenerate, etc. With Stable Diffusion, you have a lot more in your control, which also means there's a lot more to get wrong. But most models have a recommended configuration you can follow, such as NoobAI, one of the popular anime models for Stable Diffusion right now, recommending the sampler Euler at 28-35 steps and a prompt adherence of 4-5. You also need HiRes models for upscaling, ADetailer for detailing face and hands, and inpainting for fixing up small details the machine got wrong. Those aspects of generating pictures, which are quite straightforward in NovelAI, are a bit more tricky in Stable Diffusion. But just a little bit more. Once you get used to it, it becomes second nature.
tl;dr: I recommend Stable Diffusion (Forge) initially because it's free (as long as you can run it), but if you have a hard time with it and can't get it to work properly, there's NovelAI, which is easier to use and more straightforward, albeit more costly and limited.