Lightning vs LCM

I have run a short test comparing the lightning 4 step lora vs the lcm lora (also at 4 steps).

These are my observations / thoughts, unordered but hopefully helpful to assess whether Lightning or LCM are better suited for the task.

I have intentionally left out turbo as I consider it being completely superseded by Lightning.

Setup

Lightning: https://huggingface.co/ByteDance/SDXL-Lightning

LCM: https://huggingface.co/latent-consistency/lcm-lora-sdxl

Base Model: https://civitai.com/models/153128/the-allys-mix-x-sdxl?modelVersionId=171454

Workflow in ComfyUI: attached

Prompt: "A girl smiling by Josephine Wall"

Explanations:

I have chose Ally's SDXL mix due to its supreme prompt adherence. The prompt is from the Lightning default Lora workflow on HF. I have added Josephine Wall as artist due to the high amount of details being produced by adding her name to the prompt.

Observations

Lightning seems optimized towards aesthetically pleasing images achieving high scores in the common benchmarks
At 4 steps CFG between 1 and 1.5 images look more finished compared to what lcm produces
This is achieved by higher saturation, contrast and sharpness compared to LCM
This does not necessarily mean images are clearly "better". It is super-easy to increase these three image parameters post generation and then LCM images would have the same overall look.
But:
Lightning is better at larger details (parameters "b" in Freeu)
LCM is better at fine details (parameters "s" in Freeu)
Lightning offers the option to use different samplers and it works with regular and ancestral samplers likewise. The effect of the sampler is less compared to sampling with regular models (i.e. no Lightning/LCM Lora applied)

Conclusion

Depending on the use case it could be still appropriate to use LCM. For basic image generation I would definitely recommend Lightning in most cases unless you aim for more fine-grained details. For upscaling images LCM might be able to outshine Lightning still by adding more useful and finer details, it is up to another test.

Overall I am impressed with the quality Lightning is capable to produce.