Site like the main Stable Diffusion hosting site or Google Workbooks for these training models are nice but tend to be a lot of hassle to even get started.
In the case of the main Stable Diffusion site it only really has Stable Diffusion; duh.
Models like Midjourney and the other more tweaked ones all have usage limits and they are rather low, there are some which do give even better limits than Midjourney but you will likely always hit a cap.
So basically none are free forever and if they are they are rather shitty.
InstantArt.io
InstantArt does make an attempt at changing that, they are free forever - as far as right now is concerned; they are not all that shitty.
Some patience will be required though, and I think with the surge of users wanting something completely free there will be plenty of growing pains.
InstantArt does provide quite a few different AI models to choose from including ones that aim to be more like Midjourney, or one that is trained only on robot style things, Wifu Anime art styles and things like that.
I wanted to do quite a few different ones of the same style but it could be that I am trying at some peak period. What happens then is it will say your Text Prompt has been submitted and show these generating image placeholders.
I am yet to see one of them turn into an image. So for all intents and purpose I will assume if I get those it is broken.
It does generate images and I think if they are not overloaded then you can play without too many concerns, test out different models and more importantly really try to get the prompts just right.
I don't actually know if prompting has changed much but where Disco Diffusion and Stable Diffusion tended to try and put everything into the image I mentioned; this one kinda picked and chooses.
There is a contrast setting so possibly it is just that I had it a bit lax.
As you can see in the prompt there should be a boy with dragon wings... Maybe there is , maybe the boy is a dragonfly deep in the image.
The image as a whole though is very good and if I get use to what prompt styles the model likes it would be smooth sailing.
So although you might not be able to generate anything due to scaling issues on InstantArt it is definitely a versatile AI art sandbox tool to add to the myriad of tools you might already be using.